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 $60.70   13.410%   $68.8399   $68.84   $68.85   $68.80  
  Purchase #2 $57.44   10.110%   $63.2472   $63.25   $63.25   $63.20  
  Purchase #3 $19.96   6.494%   $21.2562   $21.26   $21.25   $21.30  
  Purchase #4 $127.78   12.520%   $143.7781   $143.78   $143.80   $143.80  
  Purchase #5 $117.75   4.604%   $123.1712   $123.17   $123.15   $123.20  
  Purchase #6 $161.44   10.266%   $178.0134   $178.01   $178.00   $178.00  
  Purchase #7 $224.79   7.542%   $241.7437   $241.74   $241.75   $241.70  
  7 purchase totals = $769.86       $840.0497   $840.05   $840.05   $840.00