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	$50.54	9.626%	$55.405	$55.41	$55.40	$55.40
Purchase #2	$130.34	12.569%	$146.7224	$146.72	$146.70	$146.70
Purchase #3	$236.98	13.645%	$269.3159	$269.32	$269.30	$269.30
Purchase #4	$79.78	6.826%	$85.2258	$85.23	$85.25	$85.20
Purchase #5	$196.97	11.657%	$219.9308	$219.93	$219.95	$219.90
Purchase #6	$190.72	12.267%	$214.1156	$214.12	$214.10	$214.10
Purchase #7	$142.33	4.443%	$148.6537	$148.65	$148.65	$148.70
7 purchase totals =	$1,027.66		$1,139.3692	$1,139.38	$1,139.35	$1,139.30