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	$32.97	12.668%	$37.1466	$37.15	$37.15	$37.10
Purchase #2	$137.46	4.342%	$143.4285	$143.43	$143.45	$143.40
Purchase #3	$151.91	9.468%	$166.2928	$166.29	$166.30	$166.30
Purchase #4	$7.59	9.237%	$8.2911	$8.29	$8.30	$8.30
Purchase #5	$65.44	3.208%	$67.5393	$67.54	$67.55	$67.50
Purchase #6	$190.45	6.292%	$202.4331	$202.43	$202.45	$202.40
Purchase #7	$170.69	8.750%	$185.6254	$185.63	$185.65	$185.60
7 purchase totals =	$756.51		$810.7568	$810.76	$810.85	$810.60