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 $218.66   8.517%   $237.2833   $237.28   $237.30   $237.30  
  Purchase #2 $163.89   5.417%   $172.7679   $172.77   $172.75   $172.80  
  Purchase #3 $222.82   9.780%   $244.6118   $244.61   $244.60   $244.60  
  Purchase #4 $94.92   3.804%   $98.5308   $98.53   $98.55   $98.50  
  Purchase #5 $186.66   9.770%   $204.8967   $204.90   $204.90   $204.90  
  Purchase #6 $39.78   12.820%   $44.8798   $44.88   $44.90   $44.90  
  Purchase #7 $19.81   10.712%   $21.932   $21.93   $21.95   $21.90  
  7 purchase totals = $946.54       $1,024.9023   $1,024.90   $1,024.95   $1,024.90