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 $59.90   10.113%   $65.9577   $65.96   $65.95   $66.00  
  Purchase #2 $97.36   6.404%   $103.5949   $103.59   $103.60   $103.60  
  Purchase #3 $26.63   9.376%   $29.1268   $29.13   $29.15   $29.10  
  Purchase #4 $133.98   10.829%   $148.4887   $148.49   $148.50   $148.50  
  Purchase #5 $204.58   9.190%   $223.3809   $223.38   $223.40   $223.40  
  Purchase #6 $105.88   4.119%   $110.2412   $110.24   $110.25   $110.20  
  Purchase #7 $61.49   11.214%   $68.3855   $68.39   $68.40   $68.40  
  7 purchase totals = $689.82       $749.1757   $749.18   $749.25   $749.20