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 $57.95   11.792%   $64.7835   $64.78   $64.80   $64.80  
  Purchase #2 $106.83   6.652%   $113.9363   $113.94   $113.95   $113.90  
  Purchase #3 $24.53   6.524%   $26.1303   $26.13   $26.15   $26.10  
  Purchase #4 $63.25   6.410%   $67.3043   $67.30   $67.30   $67.30  
  Purchase #5 $195.36   3.645%   $202.4809   $202.48   $202.50   $202.50  
  Purchase #6 $15.85   9.148%   $17.3   $17.30   $17.30   $17.30  
  Purchase #7 $110.66   11.808%   $123.7267   $123.73   $123.75   $123.70  
  7 purchase totals = $574.43       $615.6620   $615.66   $615.75   $615.60