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 $96.77   6.449%   $103.0107   $103.01   $103.00   $103.00  
  Purchase #2 $233.94   4.863%   $245.3165   $245.32   $245.30   $245.30  
  Purchase #3 $26.25   8.712%   $28.5369   $28.54   $28.55   $28.50  
  Purchase #4 $229.58   13.241%   $259.9787   $259.98   $260.00   $260.00  
  Purchase #5 $60.89   8.159%   $65.858   $65.86   $65.85   $65.90  
  Purchase #6 $134.44   5.483%   $141.8113   $141.81   $141.80   $141.80  
  Purchase #7 $204.83   11.439%   $228.2605   $228.26   $228.25   $228.30  
  7 purchase totals = $986.70       $1,072.7726   $1,072.78   $1,072.75   $1,072.80