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 $58.91   5.300%   $62.0322   $62.03   $62.05   $62.00  
  Purchase #2 $117.46   4.643%   $122.9137   $122.91   $122.90   $122.90  
  Purchase #3 $195.71   7.742%   $210.8619   $210.86   $210.85   $210.90  
  Purchase #4 $39.29   7.622%   $42.2847   $42.28   $42.30   $42.30  
  Purchase #5 $210.83   5.870%   $223.2057   $223.21   $223.20   $223.20  
  Purchase #6 $164.41   10.533%   $181.7273   $181.73   $181.75   $181.70  
  Purchase #7 $75.52   4.220%   $78.7069   $78.71   $78.70   $78.70  
  7 purchase totals = $862.13       $921.7324   $921.73   $921.75   $921.70