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 $65.86   8.508%   $71.4634   $71.46   $71.45   $71.50  
  Purchase #2 $190.51   6.478%   $202.8512   $202.85   $202.85   $202.90  
  Purchase #3 $28.88   4.613%   $30.2122   $30.21   $30.20   $30.20  
  Purchase #4 $123.75   8.711%   $134.5299   $134.53   $134.55   $134.50  
  Purchase #5 $37.35   6.198%   $39.665   $39.67   $39.65   $39.70  
  Purchase #6 $164.83   11.478%   $183.7492   $183.75   $183.75   $183.70  
  Purchase #7 $24.43   3.120%   $25.1922   $25.19   $25.20   $25.20  
  7 purchase totals = $635.61       $687.6631   $687.66   $687.65   $687.70