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 $88.65   6.587%   $94.4894   $94.49   $94.50   $94.50  
  Purchase #2 $249.31   4.540%   $260.6287   $260.63   $260.65   $260.60  
  Purchase #3 $106.36   3.646%   $110.2379   $110.24   $110.25   $110.20  
  Purchase #4 $140.26   10.832%   $155.453   $155.45   $155.45   $155.50  
  Purchase #5 $94.61   4.354%   $98.7293   $98.73   $98.75   $98.70  
  Purchase #6 $82.61   7.288%   $88.6306   $88.63   $88.65   $88.60  
  Purchase #7 $211.87   11.317%   $235.8473   $235.85   $235.85   $235.80  
  7 purchase totals = $973.67       $1,044.0162   $1,044.02   $1,044.10   $1,043.90