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	$73.73	10.527%	$81.4916	$81.49	$81.50	$81.50
Purchase #2	$244.80	4.265%	$255.2407	$255.24	$255.25	$255.20
Purchase #3	$170.97	10.823%	$189.4741	$189.47	$189.45	$189.50
Purchase #4	$99.27	10.705%	$109.8969	$109.90	$109.90	$109.90
Purchase #5	$74.67	4.394%	$77.951	$77.95	$77.95	$78.00
Purchase #6	$240.89	6.530%	$256.6201	$256.62	$256.60	$256.60
Purchase #7	$88.92	7.172%	$95.2973	$95.30	$95.30	$95.30
7 purchase totals =	$993.25		$1,065.9717	$1,065.97	$1,065.95	$1,066.00