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	$106.46	3.588%	$110.2798	$110.28	$110.30	$110.30
Purchase #2	$85.82	5.105%	$90.2011	$90.20	$90.20	$90.20
Purchase #3	$140.77	13.345%	$159.5558	$159.56	$159.55	$159.60
Purchase #4	$148.45	7.664%	$159.8272	$159.83	$159.85	$159.80
Purchase #5	$114.75	5.212%	$120.7308	$120.73	$120.75	$120.70
Purchase #6	$128.80	9.675%	$141.2614	$141.26	$141.25	$141.30
Purchase #7	$47.38	12.399%	$53.2546	$53.25	$53.25	$53.30
7 purchase totals =	$772.43		$835.1107	$835.11	$835.15	$835.20