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 $68.74   7.252%   $73.725   $73.73   $73.75   $73.70  
  Purchase #2 $146.95   13.618%   $166.9617   $166.96   $166.95   $167.00  
  Purchase #3 $185.41   11.236%   $206.2427   $206.24   $206.25   $206.20  
  Purchase #4 $19.38   3.315%   $20.0224   $20.02   $20.00   $20.00  
  Purchase #5 $30.38   4.865%   $31.858   $31.86   $31.85   $31.90  
  Purchase #6 $219.93   4.775%   $230.4317   $230.43   $230.45   $230.40  
  Purchase #7 $6.93   4.249%   $7.2245   $7.22   $7.20   $7.20  
  7 purchase totals = $677.72       $736.4660   $736.46   $736.45   $736.40