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 $59.94   8.241%   $64.8797   $64.88   $64.90   $64.90  
  Purchase #2 $6.39   9.229%   $6.9797   $6.98   $7.00   $7.00  
  Purchase #3 $190.87   7.520%   $205.2234   $205.22   $205.20   $205.20  
  Purchase #4 $137.79   7.310%   $147.8624   $147.86   $147.85   $147.90  
  Purchase #5 $219.29   11.861%   $245.3   $245.30   $245.30   $245.30  
  Purchase #6 $71.47   8.497%   $77.5428   $77.54   $77.55   $77.50  
  Purchase #7 $208.49   6.421%   $221.8771   $221.88   $221.90   $221.90  
  7 purchase totals = $894.24       $969.6651   $969.66   $969.70   $969.70