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 $55.52   5.769%   $58.7229   $58.72   $58.70   $58.70  
  Purchase #2 $88.71   5.192%   $93.3158   $93.32   $93.30   $93.30  
  Purchase #3 $247.50   8.854%   $269.4137   $269.41   $269.40   $269.40  
  Purchase #4 $71.70   9.524%   $78.5287   $78.53   $78.55   $78.50  
  Purchase #5 $84.46   12.871%   $95.3308   $95.33   $95.35   $95.30  
  Purchase #6 $213.84   13.618%   $242.9607   $242.96   $242.95   $243.00  
  Purchase #7 $173.30   9.507%   $189.7756   $189.78   $189.80   $189.80  
  7 purchase totals = $935.03       $1,028.0482   $1,028.05   $1,028.05   $1,028.00