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	$146.39	3.322%	$151.2531	$151.25	$151.25	$151.30
Purchase #2	$30.39	5.656%	$32.1089	$32.11	$32.10	$32.10
Purchase #3	$143.83	10.797%	$159.3593	$159.36	$159.35	$159.40
Purchase #4	$74.72	9.794%	$82.0381	$82.04	$82.05	$82.00
Purchase #5	$15.53	5.851%	$16.4387	$16.44	$16.45	$16.40
Purchase #6	$85.39	4.478%	$89.2138	$89.21	$89.20	$89.20
Purchase #7	$146.66	3.838%	$152.2888	$152.29	$152.30	$152.30
7 purchase totals =	$642.91		$682.7007	$682.70	$682.70	$682.70