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 $92.92   9.276%   $101.5393   $101.54   $101.55   $101.50  
  Purchase #2 $88.99   9.333%   $97.2954   $97.30   $97.30   $97.30  
  Purchase #3 $119.35   5.569%   $125.9966   $126.00   $126.00   $126.00  
  Purchase #4 $138.83   10.678%   $153.6543   $153.65   $153.65   $153.70  
  Purchase #5 $213.41   6.730%   $227.7725   $227.77   $227.75   $227.80  
  Purchase #6 $149.66   12.190%   $167.9036   $167.90   $167.90   $167.90  
  Purchase #7 $240.44   10.558%   $265.8257   $265.83   $265.85   $265.80  
  7 purchase totals = $1,043.60       $1,139.9874   $1,139.99   $1,140.00   $1,140.00