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 $191.93   6.156%   $203.7452   $203.75   $203.75   $203.70  
  Purchase #2 $10.64   7.524%   $11.4406   $11.44   $11.45   $11.40  
  Purchase #3 $118.73   8.724%   $129.088   $129.09   $129.10   $129.10  
  Purchase #4 $13.51   13.251%   $15.3002   $15.30   $15.30   $15.30  
  Purchase #5 $62.77   5.647%   $66.3146   $66.31   $66.30   $66.30  
  Purchase #6 $148.39   5.757%   $156.9328   $156.93   $156.95   $156.90  
  Purchase #7 $200.32   10.390%   $221.1332   $221.13   $221.15   $221.10  
  7 purchase totals = $746.29       $803.9546   $803.95   $804.00   $803.80