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 $244.87   6.523%   $260.8429   $260.84   $260.85   $260.80  
  Purchase #2 $80.89   10.378%   $89.2848   $89.28   $89.30   $89.30  
  Purchase #3 $16.36   10.748%   $18.1184   $18.12   $18.10   $18.10  
  Purchase #4 $93.29   9.597%   $102.243   $102.24   $102.25   $102.20  
  Purchase #5 $145.42   3.842%   $151.007   $151.01   $151.00   $151.00  
  Purchase #6 $109.63   9.697%   $120.2608   $120.26   $120.25   $120.30  
  Purchase #7 $118.32   5.203%   $124.4762   $124.48   $124.50   $124.50  
  7 purchase totals = $808.78       $866.2331   $866.23   $866.25   $866.20