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 $88.56   10.139%   $97.5391   $97.54   $97.55   $97.50  
  Purchase #2 $204.97   12.199%   $229.9743   $229.97   $229.95   $230.00  
  Purchase #3 $17.82   7.856%   $19.2199   $19.22   $19.20   $19.20  
  Purchase #4 $213.26   10.480%   $235.6096   $235.61   $235.60   $235.60  
  Purchase #5 $13.66   6.869%   $14.5983   $14.60   $14.60   $14.60  
  Purchase #6 $122.44   6.827%   $130.799   $130.80   $130.80   $130.80  
  Purchase #7 $110.82   6.138%   $117.6221   $117.62   $117.60   $117.60  
  7 purchase totals = $771.53       $845.3623   $845.36   $845.30   $845.30