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 $65.83   7.460%   $70.7409   $70.74   $70.75   $70.70  
  Purchase #2 $243.72   6.294%   $259.0597   $259.06   $259.05   $259.10  
  Purchase #3 $204.33   6.541%   $217.6952   $217.70   $217.70   $217.70  
  Purchase #4 $93.40   7.695%   $100.5871   $100.59   $100.60   $100.60  
  Purchase #5 $182.69   5.854%   $193.3847   $193.38   $193.40   $193.40  
  Purchase #6 $91.49   5.429%   $96.457   $96.46   $96.45   $96.50  
  Purchase #7 $242.57   9.725%   $266.1599   $266.16   $266.15   $266.20  
  7 purchase totals = $1,124.03       $1,204.0845   $1,204.09   $1,204.10   $1,204.20