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 $68.47   12.121%   $76.7692   $76.77   $76.75   $76.80  
  Purchase #2 $215.48   4.409%   $224.9805   $224.98   $225.00   $225.00  
  Purchase #3 $171.55   7.661%   $184.6924   $184.69   $184.70   $184.70  
  Purchase #4 $234.36   3.424%   $242.3845   $242.38   $242.40   $242.40  
  Purchase #5 $52.85   3.110%   $54.4936   $54.49   $54.50   $54.50  
  Purchase #6 $75.56   4.106%   $78.6625   $78.66   $78.65   $78.70  
  Purchase #7 $173.32   7.347%   $186.0538   $186.05   $186.05   $186.10  
  7 purchase totals = $991.59       $1,048.0365   $1,048.02   $1,048.05   $1,048.20