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	$165.62	3.795%	$171.9053	$171.91	$171.90	$171.90
Purchase #2	$99.87	6.652%	$106.5134	$106.51	$106.50	$106.50
Purchase #3	$109.76	8.223%	$118.7856	$118.79	$118.80	$118.80
Purchase #4	$53.58	5.542%	$56.5494	$56.55	$56.55	$56.50
Purchase #5	$136.93	12.276%	$153.7395	$153.74	$153.75	$153.70
Purchase #6	$40.71	4.762%	$42.6486	$42.65	$42.65	$42.60
Purchase #7	$104.67	9.429%	$114.5393	$114.54	$114.55	$114.50
7 purchase totals =	$711.14		$764.6811	$764.69	$764.70	$764.50