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 $239.87   12.442%   $269.7146   $269.71   $269.70   $269.70  
  Purchase #2 $114.94   12.471%   $129.2742   $129.27   $129.25   $129.30  
  Purchase #3 $50.52   13.410%   $57.2947   $57.29   $57.30   $57.30  
  Purchase #4 $190.41   10.817%   $211.0066   $211.01   $211.00   $211.00  
  Purchase #5 $18.64   5.420%   $19.6503   $19.65   $19.65   $19.70  
  Purchase #6 $247.45   12.200%   $277.6389   $277.64   $277.65   $277.60  
  Purchase #7 $58.32   6.293%   $61.9901   $61.99   $62.00   $62.00  
  7 purchase totals = $920.15       $1,026.5694   $1,026.56   $1,026.55   $1,026.60