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 $191.82   6.619%   $204.5166   $204.52   $204.50   $204.50  
  Purchase #2 $41.64   4.633%   $43.5692   $43.57   $43.55   $43.60  
  Purchase #3 $248.68   6.108%   $263.8694   $263.87   $263.85   $263.90  
  Purchase #4 $202.76   13.347%   $229.8224   $229.82   $229.80   $229.80  
  Purchase #5 $107.70   8.271%   $116.6079   $116.61   $116.60   $116.60  
  Purchase #6 $105.88   10.469%   $116.9646   $116.96   $116.95   $117.00  
  Purchase #7 $122.60   11.174%   $136.2993   $136.30   $136.30   $136.30  
  7 purchase totals = $1,021.08       $1,111.6494   $1,111.65   $1,111.55   $1,111.70