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	$84.89	5.866%	$89.8696	$89.87	$89.85	$89.90
Purchase #2	$150.39	3.459%	$155.592	$155.59	$155.60	$155.60
Purchase #3	$13.84	9.254%	$15.1208	$15.12	$15.10	$15.10
Purchase #4	$236.61	9.214%	$258.4112	$258.41	$258.40	$258.40
Purchase #5	$50.84	6.404%	$54.0958	$54.10	$54.10	$54.10
Purchase #6	$79.74	10.608%	$88.1988	$88.20	$88.20	$88.20
Purchase #7	$40.99	11.742%	$45.803	$45.80	$45.80	$45.80
7 purchase totals =	$657.30		$707.0912	$707.09	$707.05	$707.10