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 $191.39   10.728%   $211.9223   $211.92   $211.90   $211.90  
  Purchase #2 $64.39   8.670%   $69.9726   $69.97   $69.95   $70.00  
  Purchase #3 $20.43   9.384%   $22.3472   $22.35   $22.35   $22.30  
  Purchase #4 $202.67   9.160%   $221.2346   $221.23   $221.25   $221.20  
  Purchase #5 $46.53   10.248%   $51.2984   $51.30   $51.30   $51.30  
  Purchase #6 $125.77   11.805%   $140.6171   $140.62   $140.60   $140.60  
  Purchase #7 $101.86   9.648%   $111.6875   $111.69   $111.70   $111.70  
  7 purchase totals = $753.04       $829.0797   $829.08   $829.05   $829.00