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	$98.72	5.191%	$103.8446	$103.84	$103.85	$103.80
Purchase #2	$31.88	7.637%	$34.3147	$34.31	$34.30	$34.30
Purchase #3	$131.48	4.398%	$137.2625	$137.26	$137.25	$137.30
Purchase #4	$127.33	7.155%	$136.4405	$136.44	$136.45	$136.40
Purchase #5	$122.87	7.385%	$131.9439	$131.94	$131.95	$131.90
Purchase #6	$229.46	10.543%	$253.652	$253.65	$253.65	$253.70
Purchase #7	$61.90	5.689%	$65.4215	$65.42	$65.40	$65.40
7 purchase totals =	$803.64		$862.8797	$862.86	$862.85	$862.80