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 $68.49   12.165%   $76.8218   $76.82   $76.80   $76.80  
  Purchase #2 $72.51   8.419%   $78.6146   $78.61   $78.60   $78.60  
  Purchase #3 $65.50   9.764%   $71.8954   $71.90   $71.90   $71.90  
  Purchase #4 $119.31   12.417%   $134.1247   $134.12   $134.10   $134.10  
  Purchase #5 $211.89   13.190%   $239.8383   $239.84   $239.85   $239.80  
  Purchase #6 $117.39   3.735%   $121.7745   $121.77   $121.75   $121.80  
  Purchase #7 $53.93   11.254%   $59.9993   $60.00   $60.00   $60.00  
  7 purchase totals = $709.02       $783.0686   $783.06   $783.00   $783.00