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 $238.86   6.762%   $255.0117   $255.01   $255.00   $255.00  
  Purchase #2 $105.49   4.151%   $109.8689   $109.87   $109.85   $109.90  
  Purchase #3 $160.45   3.633%   $166.2791   $166.28   $166.30   $166.30  
  Purchase #4 $53.71   13.463%   $60.941   $60.94   $60.95   $60.90  
  Purchase #5 $219.40   7.658%   $236.2017   $236.20   $236.20   $236.20  
  Purchase #6 $164.25   7.789%   $177.0434   $177.04   $177.05   $177.00  
  Purchase #7 $33.86   4.452%   $35.3674   $35.37   $35.35   $35.40  
  7 purchase totals = $976.02       $1,040.7132   $1,040.71   $1,040.70   $1,040.70