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 $202.96   6.642%   $216.4406   $216.44   $216.45   $216.40  
  Purchase #2 $188.92   5.617%   $199.5316   $199.53   $199.55   $199.50  
  Purchase #3 $107.91   10.794%   $119.5578   $119.56   $119.55   $119.60  
  Purchase #4 $177.95   4.800%   $186.4916   $186.49   $186.50   $186.50  
  Purchase #5 $115.74   6.599%   $123.3777   $123.38   $123.40   $123.40  
  Purchase #6 $138.84   10.393%   $153.2696   $153.27   $153.25   $153.30  
  Purchase #7 $8.42   6.607%   $8.9763   $8.98   $9.00   $9.00  
  7 purchase totals = $940.74       $1,007.6452   $1,007.65   $1,007.70   $1,007.70