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 $129.97   8.690%   $141.2644   $141.26   $141.25   $141.30  
  Purchase #2 $93.52   11.715%   $104.4759   $104.48   $104.50   $104.50  
  Purchase #3 $154.89   9.231%   $169.1879   $169.19   $169.20   $169.20  
  Purchase #4 $178.66   11.845%   $199.8223   $199.82   $199.80   $199.80  
  Purchase #5 $166.95   5.411%   $175.9837   $175.98   $176.00   $176.00  
  Purchase #6 $222.29   9.247%   $242.8452   $242.85   $242.85   $242.80  
  Purchase #7 $156.79   8.153%   $169.5731   $169.57   $169.55   $169.60  
  7 purchase totals = $1,103.07       $1,203.1525   $1,203.15   $1,203.15   $1,203.20