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 $98.67   13.467%   $111.9579   $111.96   $111.95   $112.00  
  Purchase #2 $112.32   5.204%   $118.1651   $118.17   $118.15   $118.20  
  Purchase #3 $49.52   7.431%   $53.1998   $53.20   $53.20   $53.20  
  Purchase #4 $177.64   13.743%   $202.0531   $202.05   $202.05   $202.10  
  Purchase #5 $182.68   6.224%   $194.05   $194.05   $194.05   $194.10  
  Purchase #6 $82.91   13.372%   $93.9967   $94.00   $94.00   $94.00  
  Purchase #7 $150.97   4.321%   $157.4934   $157.49   $157.50   $157.50  
  7 purchase totals = $854.71       $930.9160   $930.92   $930.90   $931.10