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	$131.82	8.794%	$143.4123	$143.41	$143.40	$143.40
Purchase #2	$39.39	7.513%	$42.3494	$42.35	$42.35	$42.30
Purchase #3	$159.64	7.146%	$171.0479	$171.05	$171.05	$171.00
Purchase #4	$53.45	11.863%	$59.7908	$59.79	$59.80	$59.80
Purchase #5	$184.68	12.147%	$207.1131	$207.11	$207.10	$207.10
Purchase #6	$18.35	13.736%	$20.8706	$20.87	$20.85	$20.90
Purchase #7	$50.59	8.439%	$54.8593	$54.86	$54.85	$54.90
7 purchase totals =	$637.92		$699.4434	$699.44	$699.40	$699.40