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 $129.46   12.133%   $145.1674   $145.17   $145.15   $145.20  
  Purchase #2 $199.98   4.296%   $208.5711   $208.57   $208.55   $208.60  
  Purchase #3 $95.84   8.608%   $104.0899   $104.09   $104.10   $104.10  
  Purchase #4 $30.53   13.440%   $34.6332   $34.63   $34.65   $34.60  
  Purchase #5 $191.33   13.718%   $217.5766   $217.58   $217.60   $217.60  
  Purchase #6 $88.96   3.432%   $92.0131   $92.01   $92.00   $92.00  
  Purchase #7 $149.44   8.125%   $161.582   $161.58   $161.60   $161.60  
  7 purchase totals = $885.54       $963.6333   $963.63   $963.65   $963.70