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 $174.58   11.317%   $194.3372   $194.34   $194.35   $194.30  
  Purchase #2 $97.61   8.338%   $105.7487   $105.75   $105.75   $105.70  
  Purchase #3 $60.98   13.567%   $69.2532   $69.25   $69.25   $69.30  
  Purchase #4 $220.38   6.549%   $234.8127   $234.81   $234.80   $234.80  
  Purchase #5 $112.52   12.355%   $126.4218   $126.42   $126.40   $126.40  
  Purchase #6 $209.86   10.545%   $231.9897   $231.99   $232.00   $232.00  
  Purchase #7 $75.67   7.437%   $81.2976   $81.30   $81.30   $81.30  
  7 purchase totals = $951.60       $1,043.8609   $1,043.86   $1,043.85   $1,043.80