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 $184.51   11.327%   $205.4094   $205.41   $205.40   $205.40  
  Purchase #2 $109.81   13.608%   $124.7529   $124.75   $124.75   $124.80  
  Purchase #3 $9.96   4.228%   $10.3811   $10.38   $10.40   $10.40  
  Purchase #4 $158.99   8.150%   $171.9477   $171.95   $171.95   $171.90  
  Purchase #5 $59.82   11.197%   $66.518   $66.52   $66.50   $66.50  
  Purchase #6 $66.99   11.477%   $74.6784   $74.68   $74.70   $74.70  
  Purchase #7 $161.31   8.463%   $174.9617   $174.96   $174.95   $175.00  
  7 purchase totals = $751.39       $828.6492   $828.65   $828.65   $828.70