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	$100.75	8.229%	$109.0407	$109.04	$109.05	$109.00
Purchase #2	$170.72	4.405%	$178.2402	$178.24	$178.25	$178.20
Purchase #3	$48.29	8.672%	$52.4777	$52.48	$52.50	$52.50
Purchase #4	$135.73	9.606%	$148.7682	$148.77	$148.75	$148.80
Purchase #5	$53.36	11.227%	$59.3507	$59.35	$59.35	$59.40
Purchase #6	$19.83	3.202%	$20.465	$20.47	$20.45	$20.50
Purchase #7	$86.39	6.196%	$91.7427	$91.74	$91.75	$91.70
7 purchase totals =	$615.07		$660.0852	$660.09	$660.10	$660.10