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	$248.67	9.820%	$273.0894	$273.09	$273.10	$273.10
Purchase #2	$165.77	3.869%	$172.1836	$172.18	$172.20	$172.20
Purchase #3	$42.57	12.335%	$47.821	$47.82	$47.80	$47.80
Purchase #4	$91.46	8.604%	$99.3292	$99.33	$99.35	$99.30
Purchase #5	$137.50	13.857%	$156.5534	$156.55	$156.55	$156.60
Purchase #6	$93.64	10.556%	$103.5246	$103.52	$103.50	$103.50
Purchase #7	$180.81	4.347%	$188.6698	$188.67	$188.65	$188.70
7 purchase totals =	$960.42		$1,041.1710	$1,041.16	$1,041.15	$1,041.20