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 $59.50   6.620%   $63.4389   $63.44   $63.45   $63.40  
  Purchase #2 $182.62   11.511%   $203.6414   $203.64   $203.65   $203.60  
  Purchase #3 $54.50   6.365%   $57.9689   $57.97   $57.95   $58.00  
  Purchase #4 $134.74   13.140%   $152.4448   $152.44   $152.45   $152.40  
  Purchase #5 $148.86   13.483%   $168.9308   $168.93   $168.95   $168.90  
  Purchase #6 $141.83   6.358%   $150.8476   $150.85   $150.85   $150.80  
  Purchase #7 $35.71   10.157%   $39.3371   $39.34   $39.35   $39.30  
  7 purchase totals = $757.76       $836.6095   $836.61   $836.65   $836.40