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 $249.63   5.652%   $263.7391   $263.74   $263.75   $263.70  
  Purchase #2 $134.95   12.550%   $151.8862   $151.89   $151.90   $151.90  
  Purchase #3 $203.46   11.448%   $226.7521   $226.75   $226.75   $226.80  
  Purchase #4 $167.26   5.115%   $175.8153   $175.82   $175.80   $175.80  
  Purchase #5 $19.96   5.582%   $21.0742   $21.07   $21.05   $21.10  
  Purchase #6 $43.51   13.548%   $49.4047   $49.40   $49.40   $49.40  
  Purchase #7 $132.67   9.493%   $145.2644   $145.26   $145.25   $145.30  
  7 purchase totals = $951.44       $1,033.9360   $1,033.93   $1,033.90   $1,034.00