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 $215.43   13.577%   $244.6789   $244.68   $244.70   $244.70  
  Purchase #2 $103.33   12.242%   $115.9797   $115.98   $116.00   $116.00  
  Purchase #3 $243.90   4.568%   $255.0414   $255.04   $255.05   $255.00  
  Purchase #4 $135.51   13.279%   $153.5044   $153.50   $153.50   $153.50  
  Purchase #5 $52.58   8.812%   $57.2133   $57.21   $57.20   $57.20  
  Purchase #6 $26.34   7.578%   $28.336   $28.34   $28.35   $28.30  
  Purchase #7 $100.62   3.394%   $104.035   $104.04   $104.05   $104.00  
  7 purchase totals = $877.71       $958.7887   $958.79   $958.85   $958.70