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 $17.29   7.291%   $18.5506   $18.55   $18.55   $18.60  
  Purchase #2 $121.47   10.382%   $134.081   $134.08   $134.10   $134.10  
  Purchase #3 $243.82   10.356%   $269.07   $269.07   $269.05   $269.10  
  Purchase #4 $128.97   8.186%   $139.5275   $139.53   $139.55   $139.50  
  Purchase #5 $18.94   10.873%   $20.9993   $21.00   $21.00   $21.00  
  Purchase #6 $26.61   10.316%   $29.3551   $29.36   $29.35   $29.40  
  Purchase #7 $134.47   8.558%   $145.9779   $145.98   $146.00   $146.00  
  7 purchase totals = $691.57       $757.5614   $757.57   $757.60   $757.70