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 $36.81   13.651%   $41.8349   $41.83   $41.85   $41.80  
  Purchase #2 $195.48   8.327%   $211.7576   $211.76   $211.75   $211.80  
  Purchase #3 $162.97   12.159%   $182.7855   $182.79   $182.80   $182.80  
  Purchase #4 $224.79   12.505%   $252.9   $252.90   $252.90   $252.90  
  Purchase #5 $186.39   11.776%   $208.3393   $208.34   $208.35   $208.30  
  Purchase #6 $22.75   9.516%   $24.9149   $24.91   $24.90   $24.90  
  Purchase #7 $129.52   7.233%   $138.8882   $138.89   $138.90   $138.90  
  7 purchase totals = $958.71       $1,061.4204   $1,061.42   $1,061.45   $1,061.40