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	$133.56	13.112%	$151.0724	$151.07	$151.05	$151.10
Purchase #2	$170.99	8.546%	$185.6028	$185.60	$185.60	$185.60
Purchase #3	$131.31	10.743%	$145.4166	$145.42	$145.40	$145.40
Purchase #4	$187.93	11.112%	$208.8128	$208.81	$208.80	$208.80
Purchase #5	$150.47	6.196%	$159.7931	$159.79	$159.80	$159.80
Purchase #6	$86.69	3.134%	$89.4069	$89.41	$89.40	$89.40
Purchase #7	$52.42	6.609%	$55.8844	$55.88	$55.90	$55.90
7 purchase totals =	$913.37		$995.9890	$995.98	$995.95	$996.00