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 $23.57   11.436%   $26.2655   $26.27   $26.25   $26.30  
  Purchase #2 $174.78   5.259%   $183.9717   $183.97   $183.95   $184.00  
  Purchase #3 $66.38   13.520%   $75.3546   $75.35   $75.35   $75.40  
  Purchase #4 $239.80   8.600%   $260.4228   $260.42   $260.40   $260.40  
  Purchase #5 $103.86   13.137%   $117.5041   $117.50   $117.50   $117.50  
  Purchase #6 $145.39   9.190%   $158.7513   $158.75   $158.75   $158.80  
  Purchase #7 $226.51   8.133%   $244.9321   $244.93   $244.95   $244.90  
  7 purchase totals = $980.29       $1,067.2021   $1,067.19   $1,067.15   $1,067.30