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	$77.96	6.467%	$83.0017	$83.00	$83.00	$83.00
Purchase #2	$215.46	10.679%	$238.469	$238.47	$238.45	$238.50
Purchase #3	$56.66	10.769%	$62.7617	$62.76	$62.75	$62.80
Purchase #4	$90.61	10.121%	$99.7806	$99.78	$99.80	$99.80
Purchase #5	$191.49	9.655%	$209.9784	$209.98	$210.00	$210.00
Purchase #6	$72.58	10.872%	$80.4709	$80.47	$80.45	$80.50
Purchase #7	$102.62	11.842%	$114.7723	$114.77	$114.75	$114.80
7 purchase totals =	$807.38		$889.2346	$889.23	$889.20	$889.40