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 $94.65   10.741%   $104.8164   $104.82   $104.80   $104.80  
  Purchase #2 $97.91   10.529%   $108.2189   $108.22   $108.20   $108.20  
  Purchase #3 $57.43   3.811%   $59.6187   $59.62   $59.60   $59.60  
  Purchase #4 $67.99   9.775%   $74.636   $74.64   $74.65   $74.60  
  Purchase #5 $27.94   3.218%   $28.8391   $28.84   $28.85   $28.80  
  Purchase #6 $211.52   13.811%   $240.733   $240.73   $240.75   $240.70  
  Purchase #7 $60.98   3.361%   $63.0295   $63.03   $63.05   $63.00  
  7 purchase totals = $618.42       $679.8916   $679.90   $679.90   $679.70