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 $216.61   9.148%   $236.4255   $236.43   $236.45   $236.40  
  Purchase #2 $186.50   9.146%   $203.5573   $203.56   $203.55   $203.60  
  Purchase #3 $249.39   3.386%   $257.8343   $257.83   $257.85   $257.80  
  Purchase #4 $166.46   11.681%   $185.9042   $185.90   $185.90   $185.90  
  Purchase #5 $149.60   8.612%   $162.4836   $162.48   $162.50   $162.50  
  Purchase #6 $11.59   5.447%   $12.2213   $12.22   $12.20   $12.20  
  Purchase #7 $126.79   7.629%   $136.4628   $136.46   $136.45   $136.50  
  7 purchase totals = $1,106.94       $1,194.8890   $1,194.88   $1,194.90   $1,194.90