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 $204.79   8.488%   $222.1726   $222.17   $222.15   $222.20  
  Purchase #2 $32.60   5.184%   $34.29   $34.29   $34.30   $34.30  
  Purchase #3 $92.57   3.263%   $95.5906   $95.59   $95.60   $95.60  
  Purchase #4 $160.92   7.803%   $173.4766   $173.48   $173.50   $173.50  
  Purchase #5 $126.88   7.169%   $135.976   $135.98   $136.00   $136.00  
  Purchase #6 $74.47   6.378%   $79.2197   $79.22   $79.20   $79.20  
  Purchase #7 $97.34   6.824%   $103.9825   $103.98   $104.00   $104.00  
  7 purchase totals = $789.57       $844.7080   $844.71   $844.75   $844.80