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 $91.38   3.166%   $94.2731   $94.27   $94.25   $94.30  
  Purchase #2 $127.98   3.633%   $132.6295   $132.63   $132.65   $132.60  
  Purchase #3 $247.49   3.234%   $255.4938   $255.49   $255.50   $255.50  
  Purchase #4 $9.84   9.309%   $10.756   $10.76   $10.75   $10.80  
  Purchase #5 $65.95   4.455%   $68.8881   $68.89   $68.90   $68.90  
  Purchase #6 $241.88   7.444%   $259.8855   $259.89   $259.90   $259.90  
  Purchase #7 $192.84   8.510%   $209.2507   $209.25   $209.25   $209.30  
  7 purchase totals = $977.36       $1,031.1767   $1,031.18   $1,031.20   $1,031.30