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 $91.42   5.833%   $96.7525   $96.75   $96.75   $96.80  
  Purchase #2 $49.83   5.265%   $52.4535   $52.45   $52.45   $52.50  
  Purchase #3 $20.26   7.406%   $21.7605   $21.76   $21.75   $21.80  
  Purchase #4 $213.91   8.623%   $232.3555   $232.36   $232.35   $232.40  
  Purchase #5 $83.49   12.371%   $93.8185   $93.82   $93.80   $93.80  
  Purchase #6 $161.33   9.314%   $176.3563   $176.36   $176.35   $176.40  
  Purchase #7 $60.91   6.544%   $64.896   $64.90   $64.90   $64.90  
  7 purchase totals = $681.15       $738.3928   $738.40   $738.35   $738.60