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	$128.54	11.396%	$143.1884	$143.19	$143.20	$143.20
Purchase #2	$95.96	3.750%	$99.5585	$99.56	$99.55	$99.60
Purchase #3	$79.42	12.788%	$89.5762	$89.58	$89.60	$89.60
Purchase #4	$242.87	12.300%	$272.743	$272.74	$272.75	$272.70
Purchase #5	$128.43	8.106%	$138.8405	$138.84	$138.85	$138.80
Purchase #6	$222.73	8.168%	$240.9226	$240.92	$240.90	$240.90
Purchase #7	$110.68	3.102%	$114.1133	$114.11	$114.10	$114.10
7 purchase totals =	$1,008.63		$1,098.9425	$1,098.94	$1,098.95	$1,098.90