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	$99.46	10.510%	$109.9132	$109.91	$109.90	$109.90
Purchase #2	$48.77	9.778%	$53.5387	$53.54	$53.55	$53.50
Purchase #3	$85.26	8.261%	$92.3033	$92.30	$92.30	$92.30
Purchase #4	$63.86	13.234%	$72.3112	$72.31	$72.30	$72.30
Purchase #5	$240.71	4.324%	$251.1183	$251.12	$251.10	$251.10
Purchase #6	$152.52	12.333%	$171.3303	$171.33	$171.35	$171.30
Purchase #7	$250.68	11.233%	$278.8389	$278.84	$278.85	$278.80
7 purchase totals =	$941.26		$1,029.3539	$1,029.35	$1,029.35	$1,029.20