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 $131.99   10.842%   $146.3004   $146.30   $146.30   $146.30  
  Purchase #2 $228.92   11.183%   $254.5201   $254.52   $254.50   $254.50  
  Purchase #3 $11.94   11.272%   $13.2859   $13.29   $13.30   $13.30  
  Purchase #4 $63.97   8.670%   $69.5162   $69.52   $69.50   $69.50  
  Purchase #5 $180.26   7.288%   $193.3973   $193.40   $193.40   $193.40  
  Purchase #6 $97.99   11.217%   $108.9815   $108.98   $109.00   $109.00  
  Purchase #7 $106.45   11.334%   $118.515   $118.52   $118.50   $118.50  
  7 purchase totals = $821.52       $904.5164   $904.53   $904.50   $904.50