Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $233.51   5.416%   $246.1569   $246.16   $246.15   $246.20  
  Purchase #2 $226.89   4.836%   $237.8624   $237.86   $237.85   $237.90  
  Purchase #3 $241.44   11.739%   $269.7826   $269.78   $269.80   $269.80  
  Purchase #4 $165.82   3.447%   $171.5358   $171.54   $171.55   $171.50  
  Purchase #5 $194.61   9.449%   $212.9987   $213.00   $213.00   $213.00  
  Purchase #6 $247.62   12.269%   $278.0005   $278.00   $278.00   $278.00  
  Purchase #7 $126.86   13.749%   $144.302   $144.30   $144.30   $144.30  
  7 purchase totals = $1,436.75       $1,560.6389   $1,560.64   $1,560.65   $1,560.70