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	$93.56	9.266%	$102.2293	$102.23	$102.25	$102.20
Purchase #2	$92.61	10.702%	$102.5211	$102.52	$102.50	$102.50
Purchase #3	$97.42	4.448%	$101.7532	$101.75	$101.75	$101.80
Purchase #4	$221.53	5.374%	$233.435	$233.44	$233.45	$233.40
Purchase #5	$228.89	4.381%	$238.9177	$238.92	$238.90	$238.90
Purchase #6	$136.45	6.387%	$145.1651	$145.17	$145.15	$145.20
Purchase #7	$80.70	13.417%	$91.5275	$91.53	$91.55	$91.50
7 purchase totals =	$951.16		$1,015.5489	$1,015.56	$1,015.55	$1,015.50