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 $33.51   8.238%   $36.2706   $36.27   $36.25   $36.30  
  Purchase #2 $152.87   3.524%   $158.2571   $158.26   $158.25   $158.30  
  Purchase #3 $246.73   6.735%   $263.3473   $263.35   $263.35   $263.30  
  Purchase #4 $198.85   9.453%   $217.6473   $217.65   $217.65   $217.60  
  Purchase #5 $88.63   9.833%   $97.345   $97.35   $97.35   $97.30  
  Purchase #6 $220.48   7.830%   $237.7436   $237.74   $237.75   $237.70  
  Purchase #7 $12.47   5.282%   $13.1287   $13.13   $13.15   $13.10  
  7 purchase totals = $953.54       $1,023.7396   $1,023.75   $1,023.75   $1,023.60