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 $55.86   13.727%   $63.5279   $63.53   $63.55   $63.50  
  Purchase #2 $97.35   10.494%   $107.5659   $107.57   $107.55   $107.60  
  Purchase #3 $207.25   8.555%   $224.9802   $224.98   $225.00   $225.00  
  Purchase #4 $239.68   10.795%   $265.5535   $265.55   $265.55   $265.60  
  Purchase #5 $102.56   7.405%   $110.1546   $110.15   $110.15   $110.20  
  Purchase #6 $131.56   6.396%   $139.9746   $139.97   $139.95   $140.00  
  Purchase #7 $233.77   12.137%   $262.1427   $262.14   $262.15   $262.10  
  7 purchase totals = $1,068.03       $1,173.8994   $1,173.89   $1,173.90   $1,174.00