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	$10.55	11.446%	$11.7576	$11.76	$11.75	$11.80
Purchase #2	$37.61	7.678%	$40.4977	$40.50	$40.50	$40.50
Purchase #3	$234.94	4.521%	$245.5616	$245.56	$245.55	$245.60
Purchase #4	$33.91	3.386%	$35.0582	$35.06	$35.05	$35.10
Purchase #5	$128.34	9.460%	$140.481	$140.48	$140.50	$140.50
Purchase #6	$230.44	5.576%	$243.2893	$243.29	$243.30	$243.30
Purchase #7	$86.39	3.137%	$89.1001	$89.10	$89.10	$89.10
7 purchase totals =	$762.18		$805.7455	$805.75	$805.75	$805.90