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 $71.68   5.761%   $75.8095   $75.81   $75.80   $75.80  
  Purchase #2 $245.49   5.585%   $259.2006   $259.20   $259.20   $259.20  
  Purchase #3 $34.27   3.167%   $35.3553   $35.36   $35.35   $35.40  
  Purchase #4 $236.75   12.837%   $267.1416   $267.14   $267.15   $267.10  
  Purchase #5 $34.34   5.247%   $36.1418   $36.14   $36.15   $36.10  
  Purchase #6 $46.75   4.848%   $49.0164   $49.02   $49.00   $49.00  
  Purchase #7 $133.91   7.719%   $144.2465   $144.25   $144.25   $144.20  
  7 purchase totals = $803.19       $866.9117   $866.92   $866.90   $866.80