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 $61.64   12.276%   $69.2069   $69.21   $69.20   $69.20  
  Purchase #2 $100.60   13.145%   $113.8239   $113.82   $113.80   $113.80  
  Purchase #3 $103.56   12.113%   $116.1042   $116.10   $116.10   $116.10  
  Purchase #4 $68.42   11.310%   $76.1583   $76.16   $76.15   $76.20  
  Purchase #5 $97.48   6.737%   $104.0472   $104.05   $104.05   $104.00  
  Purchase #6 $192.34   10.464%   $212.4665   $212.47   $212.45   $212.50  
  Purchase #7 $239.83   10.185%   $264.2567   $264.26   $264.25   $264.30  
  7 purchase totals = $863.87       $956.0637   $956.07   $956.00   $956.10