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	$189.83	12.325%	$213.2265	$213.23	$213.25	$213.20
Purchase #2	$90.39	11.422%	$100.7143	$100.71	$100.70	$100.70
Purchase #3	$75.81	3.745%	$78.6491	$78.65	$78.65	$78.60
Purchase #4	$71.45	12.188%	$80.1583	$80.16	$80.15	$80.20
Purchase #5	$53.45	6.282%	$56.8077	$56.81	$56.80	$56.80
Purchase #6	$124.31	9.528%	$136.1543	$136.15	$136.15	$136.20
Purchase #7	$26.73	4.112%	$27.8291	$27.83	$27.85	$27.80
7 purchase totals =	$631.97		$693.5393	$693.54	$693.55	$693.50