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 $56.96   12.589%   $64.1307   $64.13   $64.15   $64.10  
  Purchase #2 $95.47   7.186%   $102.3305   $102.33   $102.35   $102.30  
  Purchase #3 $161.31   6.753%   $172.2033   $172.20   $172.20   $172.20  
  Purchase #4 $77.89   9.214%   $85.0668   $85.07   $85.05   $85.10  
  Purchase #5 $113.84   9.419%   $124.5626   $124.56   $124.55   $124.60  
  Purchase #6 $247.42   13.417%   $280.6163   $280.62   $280.60   $280.60  
  Purchase #7 $132.30   5.768%   $139.9311   $139.93   $139.95   $139.90  
  7 purchase totals = $885.19       $968.8413   $968.84   $968.85   $968.80