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	$33.88	10.574%	$37.4625	$37.46	$37.45	$37.50
Purchase #2	$217.25	7.465%	$233.4677	$233.47	$233.45	$233.50
Purchase #3	$68.25	13.425%	$77.4126	$77.41	$77.40	$77.40
Purchase #4	$106.57	7.664%	$114.7375	$114.74	$114.75	$114.70
Purchase #5	$158.77	8.165%	$171.7336	$171.73	$171.75	$171.70
Purchase #6	$67.40	3.467%	$69.7368	$69.74	$69.75	$69.70
Purchase #7	$40.70	3.466%	$42.1107	$42.11	$42.10	$42.10
7 purchase totals =	$692.82		$746.6614	$746.66	$746.65	$746.60