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 $34.69   5.569%   $36.6219   $36.62   $36.60   $36.60  
  Purchase #2 $66.98   9.499%   $73.3424   $73.34   $73.35   $73.30  
  Purchase #3 $55.73   7.503%   $59.9114   $59.91   $59.90   $59.90  
  Purchase #4 $88.52   9.167%   $96.6346   $96.63   $96.65   $96.60  
  Purchase #5 $125.61   8.760%   $136.6134   $136.61   $136.60   $136.60  
  Purchase #6 $140.45   8.118%   $151.8517   $151.85   $151.85   $151.90  
  Purchase #7 $201.62   5.211%   $212.1264   $212.13   $212.15   $212.10  
  7 purchase totals = $713.60       $767.1018   $767.09   $767.10   $767.00