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	$75.48	3.493%	$78.1165	$78.12	$78.10	$78.10
Purchase #2	$138.91	8.668%	$150.9507	$150.95	$150.95	$151.00
Purchase #3	$90.82	9.807%	$99.7267	$99.73	$99.75	$99.70
Purchase #4	$54.82	5.282%	$57.7156	$57.72	$57.70	$57.70
Purchase #5	$175.43	8.172%	$189.7661	$189.77	$189.75	$189.80
Purchase #6	$229.26	5.768%	$242.4837	$242.48	$242.50	$242.50
Purchase #7	$64.51	7.602%	$69.4141	$69.41	$69.40	$69.40
7 purchase totals =	$829.23		$888.1734	$888.18	$888.15	$888.20