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 $23.92   5.572%   $25.2528   $25.25   $25.25   $25.30  
  Purchase #2 $87.60   5.770%   $92.6545   $92.65   $92.65   $92.70  
  Purchase #3 $198.25   6.317%   $210.7735   $210.77   $210.75   $210.80  
  Purchase #4 $159.89   10.159%   $176.1332   $176.13   $176.15   $176.10  
  Purchase #5 $184.71   11.249%   $205.488   $205.49   $205.50   $205.50  
  Purchase #6 $81.81   13.255%   $92.6539   $92.65   $92.65   $92.70  
  Purchase #7 $187.94   6.266%   $199.7163   $199.72   $199.70   $199.70  
  7 purchase totals = $924.12       $1,002.6722   $1,002.66   $1,002.65   $1,002.80