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 $89.40   5.859%   $94.6379   $94.64   $94.65   $94.60  
  Purchase #2 $29.74   9.453%   $32.5513   $32.55   $32.55   $32.60  
  Purchase #3 $203.76   11.541%   $227.2759   $227.28   $227.30   $227.30  
  Purchase #4 $115.49   5.563%   $121.9147   $121.91   $121.90   $121.90  
  Purchase #5 $215.75   7.610%   $232.1686   $232.17   $232.15   $232.20  
  Purchase #6 $196.64   7.571%   $211.5276   $211.53   $211.55   $211.50  
  Purchase #7 $95.64   8.137%   $103.4222   $103.42   $103.40   $103.40  
  7 purchase totals = $946.42       $1,023.4982   $1,023.50   $1,023.50   $1,023.50