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	$93.97	9.108%	$102.5288	$102.53	$102.55	$102.50
Purchase #2	$123.31	13.472%	$139.9223	$139.92	$139.90	$139.90
Purchase #3	$145.41	3.685%	$150.7684	$150.77	$150.75	$150.80
Purchase #4	$53.54	5.810%	$56.6507	$56.65	$56.65	$56.70
Purchase #5	$116.77	4.755%	$122.3224	$122.32	$122.30	$122.30
Purchase #6	$144.90	4.560%	$151.5074	$151.51	$151.50	$151.50
Purchase #7	$106.36	4.298%	$110.9314	$110.93	$110.95	$110.90
7 purchase totals =	$784.26		$834.6314	$834.63	$834.60	$834.60