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	$40.45	5.475%	$42.6646	$42.66	$42.65	$42.70
Purchase #2	$28.29	6.496%	$30.1277	$30.13	$30.15	$30.10
Purchase #3	$247.58	8.765%	$269.2804	$269.28	$269.30	$269.30
Purchase #4	$105.42	4.134%	$109.7781	$109.78	$109.80	$109.80
Purchase #5	$97.39	8.129%	$105.3068	$105.31	$105.30	$105.30
Purchase #6	$113.81	4.689%	$119.1466	$119.15	$119.15	$119.10
Purchase #7	$155.79	10.659%	$172.3957	$172.40	$172.40	$172.40
7 purchase totals =	$788.73		$848.6999	$848.71	$848.75	$848.70