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 $92.95   12.629%   $104.6887   $104.69   $104.70   $104.70  
  Purchase #2 $176.39   10.174%   $194.3359   $194.34   $194.35   $194.30  
  Purchase #3 $78.88   11.241%   $87.7469   $87.75   $87.75   $87.70  
  Purchase #4 $54.70   9.823%   $60.0732   $60.07   $60.05   $60.10  
  Purchase #5 $115.44   4.765%   $120.9407   $120.94   $120.95   $120.90  
  Purchase #6 $178.57   5.497%   $188.386   $188.39   $188.40   $188.40  
  Purchase #7 $128.92   5.255%   $135.6947   $135.69   $135.70   $135.70  
  7 purchase totals = $825.85       $891.8661   $891.87   $891.90   $891.80