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 $244.26   4.293%   $254.7461   $254.75   $254.75   $254.70  
  Purchase #2 $205.84   13.522%   $233.6737   $233.67   $233.65   $233.70  
  Purchase #3 $85.32   11.129%   $94.8153   $94.82   $94.80   $94.80  
  Purchase #4 $107.88   9.851%   $118.5073   $118.51   $118.50   $118.50  
  Purchase #5 $65.92   12.666%   $74.2694   $74.27   $74.25   $74.30  
  Purchase #6 $37.50   11.249%   $41.7184   $41.72   $41.70   $41.70  
  Purchase #7 $85.25   6.829%   $91.0717   $91.07   $91.05   $91.10  
  7 purchase totals = $831.97       $908.8019   $908.81   $908.70   $908.80