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 $63.29   13.170%   $71.6253   $71.63   $71.65   $71.60  
  Purchase #2 $94.25   9.641%   $103.3366   $103.34   $103.35   $103.30  
  Purchase #3 $171.45   4.786%   $179.6556   $179.66   $179.65   $179.70  
  Purchase #4 $205.82   4.117%   $214.2936   $214.29   $214.30   $214.30  
  Purchase #5 $249.54   7.545%   $268.3678   $268.37   $268.35   $268.40  
  Purchase #6 $240.51   4.259%   $250.7533   $250.75   $250.75   $250.80  
  Purchase #7 $62.47   5.273%   $65.764   $65.76   $65.75   $65.80  
  7 purchase totals = $1,087.33       $1,153.7962   $1,153.80   $1,153.80   $1,153.90