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 $113.73   11.656%   $126.9864   $126.99   $127.00   $127.00  
  Purchase #2 $64.33   8.316%   $69.6797   $69.68   $69.70   $69.70  
  Purchase #3 $193.66   5.333%   $203.9879   $203.99   $204.00   $204.00  
  Purchase #4 $166.86   10.371%   $184.1651   $184.17   $184.15   $184.20  
  Purchase #5 $21.63   6.654%   $23.0693   $23.07   $23.05   $23.10  
  Purchase #6 $39.76   10.669%   $44.002   $44.00   $44.00   $44.00  
  Purchase #7 $118.27   3.796%   $122.7595   $122.76   $122.75   $122.80  
  7 purchase totals = $718.24       $774.6499   $774.66   $774.65   $774.80