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 $242.79   10.614%   $268.5597   $268.56   $268.55   $268.60  
  Purchase #2 $183.56   11.157%   $204.0398   $204.04   $204.05   $204.00  
  Purchase #3 $162.94   4.438%   $170.1713   $170.17   $170.15   $170.20  
  Purchase #4 $202.73   4.282%   $211.4109   $211.41   $211.40   $211.40  
  Purchase #5 $208.71   6.533%   $222.345   $222.35   $222.35   $222.30  
  Purchase #6 $131.97   12.443%   $148.391   $148.39   $148.40   $148.40  
  Purchase #7 $241.73   6.367%   $257.1209   $257.12   $257.10   $257.10  
  7 purchase totals = $1,374.43       $1,482.0386   $1,482.04   $1,482.00   $1,482.00