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 $24.88   4.598%   $26.024   $26.02   $26.00   $26.00  
  Purchase #2 $51.58   6.396%   $54.8791   $54.88   $54.90   $54.90  
  Purchase #3 $149.40   11.678%   $166.8469   $166.85   $166.85   $166.80  
  Purchase #4 $135.27   11.283%   $150.5325   $150.53   $150.55   $150.50  
  Purchase #5 $236.51   12.869%   $266.9465   $266.95   $266.95   $266.90  
  Purchase #6 $205.88   6.508%   $219.2787   $219.28   $219.30   $219.30  
  Purchase #7 $178.55   5.579%   $188.5113   $188.51   $188.50   $188.50  
  7 purchase totals = $982.07       $1,073.0190   $1,073.02   $1,073.05   $1,072.90