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 $46.66   13.507%   $52.9624   $52.96   $52.95   $53.00  
  Purchase #2 $61.69   10.775%   $68.3371   $68.34   $68.35   $68.30  
  Purchase #3 $243.90   8.774%   $265.2998   $265.30   $265.30   $265.30  
  Purchase #4 $179.51   9.381%   $196.3498   $196.35   $196.35   $196.30  
  Purchase #5 $192.51   12.855%   $217.2572   $217.26   $217.25   $217.30  
  Purchase #6 $223.65   7.192%   $239.7349   $239.73   $239.75   $239.70  
  Purchase #7 $217.93   7.692%   $234.6932   $234.69   $234.70   $234.70  
  7 purchase totals = $1,165.85       $1,274.6344   $1,274.63   $1,274.65   $1,274.60