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 $72.96   12.145%   $81.821   $81.82   $81.80   $81.80  
  Purchase #2 $13.62   3.452%   $14.0902   $14.09   $14.10   $14.10  
  Purchase #3 $110.75   5.261%   $116.5766   $116.58   $116.60   $116.60  
  Purchase #4 $74.36   3.709%   $77.118   $77.12   $77.10   $77.10  
  Purchase #5 $149.98   11.560%   $167.3177   $167.32   $167.30   $167.30  
  Purchase #6 $161.65   13.442%   $183.379   $183.38   $183.40   $183.40  
  Purchase #7 $200.69   11.229%   $223.2255   $223.23   $223.25   $223.20  
  7 purchase totals = $784.01       $863.5280   $863.54   $863.55   $863.50