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 $76.94   5.627%   $81.2694   $81.27   $81.25   $81.30  
  Purchase #2 $176.36   9.454%   $193.0331   $193.03   $193.05   $193.00  
  Purchase #3 $229.29   9.181%   $250.3411   $250.34   $250.35   $250.30  
  Purchase #4 $69.78   11.313%   $77.6742   $77.67   $77.65   $77.70  
  Purchase #5 $86.26   8.339%   $93.4532   $93.45   $93.45   $93.50  
  Purchase #6 $192.78   7.394%   $207.0342   $207.03   $207.05   $207.00  
  Purchase #7 $104.31   11.583%   $116.3922   $116.39   $116.40   $116.40  
  7 purchase totals = $935.72       $1,019.1974   $1,019.18   $1,019.20   $1,019.20