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 $25.54   3.873%   $26.5292   $26.53   $26.55   $26.50  
  Purchase #2 $79.68   9.429%   $87.193   $87.19   $87.20   $87.20  
  Purchase #3 $148.83   13.623%   $169.1051   $169.11   $169.10   $169.10  
  Purchase #4 $212.44   4.715%   $222.4565   $222.46   $222.45   $222.50  
  Purchase #5 $150.65   4.138%   $156.8839   $156.88   $156.90   $156.90  
  Purchase #6 $139.70   3.121%   $144.06   $144.06   $144.05   $144.10  
  Purchase #7 $113.65   11.741%   $126.9936   $126.99   $127.00   $127.00  
  7 purchase totals = $870.49       $933.2213   $933.22   $933.25   $933.30