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 $224.67   3.530%   $232.6009   $232.60   $232.60   $232.60  
  Purchase #2 $123.99   6.501%   $132.0506   $132.05   $132.05   $132.10  
  Purchase #3 $70.98   3.702%   $73.6077   $73.61   $73.60   $73.60  
  Purchase #4 $202.89   4.211%   $211.4337   $211.43   $211.45   $211.40  
  Purchase #5 $62.40   12.399%   $70.137   $70.14   $70.15   $70.10  
  Purchase #6 $72.98   13.289%   $82.6783   $82.68   $82.70   $82.70  
  Purchase #7 $195.83   5.181%   $205.976   $205.98   $206.00   $206.00  
  7 purchase totals = $953.74       $1,008.4842   $1,008.49   $1,008.55   $1,008.50