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 $229.84   11.687%   $256.7014   $256.70   $256.70   $256.70  
  Purchase #2 $101.90   12.281%   $114.4143   $114.41   $114.40   $114.40  
  Purchase #3 $222.66   6.317%   $236.7254   $236.73   $236.75   $236.70  
  Purchase #4 $53.73   9.733%   $58.9595   $58.96   $58.95   $59.00  
  Purchase #5 $115.76   13.841%   $131.7823   $131.78   $131.80   $131.80  
  Purchase #6 $211.83   8.298%   $229.4077   $229.41   $229.40   $229.40  
  Purchase #7 $67.93   13.409%   $77.0387   $77.04   $77.05   $77.00  
  7 purchase totals = $1,003.65       $1,105.0293   $1,105.03   $1,105.05   $1,105.00