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 $209.95   7.405%   $225.4968   $225.50   $225.50   $225.50  
  Purchase #2 $87.66   11.679%   $97.8978   $97.90   $97.90   $97.90  
  Purchase #3 $77.34   5.357%   $81.4831   $81.48   $81.50   $81.50  
  Purchase #4 $245.36   7.781%   $264.4515   $264.45   $264.45   $264.50  
  Purchase #5 $238.43   12.106%   $267.2943   $267.29   $267.30   $267.30  
  Purchase #6 $229.79   7.574%   $247.1943   $247.19   $247.20   $247.20  
  Purchase #7 $70.54   6.293%   $74.9791   $74.98   $75.00   $75.00  
  7 purchase totals = $1,159.07       $1,258.7969   $1,258.79   $1,258.85   $1,258.90