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	$172.90	11.302%	$192.4412	$192.44	$192.45	$192.40
Purchase #2	$54.32	9.185%	$59.3093	$59.31	$59.30	$59.30
Purchase #3	$48.55	12.814%	$54.7712	$54.77	$54.75	$54.80
Purchase #4	$78.51	13.500%	$89.1089	$89.11	$89.10	$89.10
Purchase #5	$159.61	11.153%	$177.4113	$177.41	$177.40	$177.40
Purchase #6	$38.30	11.683%	$42.7746	$42.77	$42.75	$42.80
Purchase #7	$68.93	7.222%	$73.9081	$73.91	$73.90	$73.90
7 purchase totals =	$621.12		$689.7246	$689.72	$689.65	$689.70