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 $228.77   13.841%   $260.4341   $260.43   $260.45   $260.40  
  Purchase #2 $202.29   6.307%   $215.0484   $215.05   $215.05   $215.00  
  Purchase #3 $52.58   10.793%   $58.255   $58.26   $58.25   $58.30  
  Purchase #4 $86.33   10.146%   $95.089   $95.09   $95.10   $95.10  
  Purchase #5 $235.75   10.106%   $259.5749   $259.57   $259.55   $259.60  
  Purchase #6 $116.53   8.342%   $126.2509   $126.25   $126.25   $126.30  
  Purchase #7 $18.89   9.752%   $20.7322   $20.73   $20.75   $20.70  
  7 purchase totals = $941.14       $1,035.3845   $1,035.38   $1,035.40   $1,035.40