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 $223.44   5.767%   $236.3258   $236.33   $236.35   $236.30  
  Purchase #2 $62.98   8.796%   $68.5197   $68.52   $68.50   $68.50  
  Purchase #3 $96.92   5.773%   $102.5152   $102.52   $102.50   $102.50  
  Purchase #4 $39.75   10.504%   $43.9253   $43.93   $43.95   $43.90  
  Purchase #5 $222.44   7.405%   $238.9117   $238.91   $238.90   $238.90  
  Purchase #6 $162.89   9.576%   $178.4883   $178.49   $178.50   $178.50  
  Purchase #7 $123.75   5.584%   $130.6602   $130.66   $130.65   $130.70  
  7 purchase totals = $932.17       $999.3462   $999.36   $999.35   $999.30