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 $65.65   5.862%   $69.4984   $69.50   $69.50   $69.50  
  Purchase #2 $51.89   11.664%   $57.9424   $57.94   $57.95   $57.90  
  Purchase #3 $183.26   7.413%   $196.8451   $196.85   $196.85   $196.80  
  Purchase #4 $140.36   8.691%   $152.5587   $152.56   $152.55   $152.60  
  Purchase #5 $134.68   4.728%   $141.0477   $141.05   $141.05   $141.00  
  Purchase #6 $109.77   8.428%   $119.0214   $119.02   $119.00   $119.00  
  Purchase #7 $32.42   8.368%   $35.1329   $35.13   $35.15   $35.10  
  7 purchase totals = $718.03       $772.0466   $772.05   $772.05   $771.90