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 $58.59   3.426%   $60.5973   $60.60   $60.60   $60.60  
  Purchase #2 $244.25   7.213%   $261.8678   $261.87   $261.85   $261.90  
  Purchase #3 $63.88   6.131%   $67.7965   $67.80   $67.80   $67.80  
  Purchase #4 $11.36   11.406%   $12.6557   $12.66   $12.65   $12.70  
  Purchase #5 $166.51   12.689%   $187.6385   $187.64   $187.65   $187.60  
  Purchase #6 $186.70   3.634%   $193.4847   $193.48   $193.50   $193.50  
  Purchase #7 $57.78   10.738%   $63.9844   $63.98   $64.00   $64.00  
  7 purchase totals = $789.07       $848.0249   $848.03   $848.05   $848.10