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	$79.68	12.468%	$89.6145	$89.61	$89.60	$89.60
Purchase #2	$131.94	6.852%	$140.9805	$140.98	$141.00	$141.00
Purchase #3	$209.96	11.772%	$234.6765	$234.68	$234.70	$234.70
Purchase #4	$60.95	6.172%	$64.7118	$64.71	$64.70	$64.70
Purchase #5	$192.39	10.340%	$212.2831	$212.28	$212.30	$212.30
Purchase #6	$51.72	7.197%	$55.4423	$55.44	$55.45	$55.40
Purchase #7	$202.57	9.826%	$222.4745	$222.47	$222.45	$222.50
7 purchase totals =	$929.21		$1,020.1832	$1,020.17	$1,020.20	$1,020.20