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	$110.91	10.721%	$122.8007	$122.80	$122.80	$122.80
Purchase #2	$222.72	12.306%	$250.1279	$250.13	$250.15	$250.10
Purchase #3	$53.30	8.377%	$57.7649	$57.76	$57.75	$57.80
Purchase #4	$115.71	11.441%	$128.9484	$128.95	$128.95	$128.90
Purchase #5	$65.55	10.570%	$72.4786	$72.48	$72.50	$72.50
Purchase #6	$48.45	9.282%	$52.9471	$52.95	$52.95	$52.90
Purchase #7	$197.46	12.543%	$222.2274	$222.23	$222.25	$222.20
7 purchase totals =	$814.10		$907.2950	$907.30	$907.35	$907.20