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	$171.86	8.129%	$185.8305	$185.83	$185.85	$185.80
Purchase #2	$120.52	4.471%	$125.9084	$125.91	$125.90	$125.90
Purchase #3	$190.26	7.386%	$204.3126	$204.31	$204.30	$204.30
Purchase #4	$50.52	10.830%	$55.9913	$55.99	$56.00	$56.00
Purchase #5	$66.32	4.767%	$69.4815	$69.48	$69.50	$69.50
Purchase #6	$78.76	13.778%	$89.6116	$89.61	$89.60	$89.60
Purchase #7	$67.53	13.329%	$76.5311	$76.53	$76.55	$76.50
7 purchase totals =	$745.77		$807.6670	$807.66	$807.70	$807.60