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 $244.78   8.365%   $265.2558   $265.26   $265.25   $265.30  
  Purchase #2 $220.62   13.674%   $250.7876   $250.79   $250.80   $250.80  
  Purchase #3 $215.66   3.858%   $223.9802   $223.98   $224.00   $224.00  
  Purchase #4 $169.26   5.646%   $178.8164   $178.82   $178.80   $178.80  
  Purchase #5 $169.48   9.769%   $186.0365   $186.04   $186.05   $186.00  
  Purchase #6 $118.39   4.761%   $124.0265   $124.03   $124.05   $124.00  
  Purchase #7 $58.35   9.327%   $63.7923   $63.79   $63.80   $63.80  
  7 purchase totals = $1,196.54       $1,292.6953   $1,292.71   $1,292.75   $1,292.70