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 $109.57   7.698%   $118.0047   $118.00   $118.00   $118.00  
  Purchase #2 $215.84   12.857%   $243.5905   $243.59   $243.60   $243.60  
  Purchase #3 $201.40   7.216%   $215.933   $215.93   $215.95   $215.90  
  Purchase #4 $199.55   13.759%   $227.0061   $227.01   $227.00   $227.00  
  Purchase #5 $5.66   8.451%   $6.1383   $6.14   $6.15   $6.10  
  Purchase #6 $64.43   11.369%   $71.755   $71.76   $71.75   $71.80  
  Purchase #7 $12.86   10.748%   $14.2422   $14.24   $14.25   $14.20  
  7 purchase totals = $809.31       $896.6698   $896.67   $896.70   $896.60