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 $144.98   13.297%   $164.258   $164.26   $164.25   $164.30  
  Purchase #2 $81.85   7.756%   $88.1983   $88.20   $88.20   $88.20  
  Purchase #3 $65.51   11.574%   $73.0921   $73.09   $73.10   $73.10  
  Purchase #4 $133.41   10.672%   $147.6475   $147.65   $147.65   $147.60  
  Purchase #5 $202.37   4.527%   $211.5313   $211.53   $211.55   $211.50  
  Purchase #6 $94.63   10.382%   $104.4545   $104.45   $104.45   $104.50  
  Purchase #7 $219.46   6.400%   $233.5054   $233.51   $233.50   $233.50  
  7 purchase totals = $942.21       $1,022.6871   $1,022.69   $1,022.70   $1,022.70