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	$16.27	12.437%	$18.2935	$18.29	$18.30	$18.30
Purchase #2	$246.94	11.483%	$275.2961	$275.30	$275.30	$275.30
Purchase #3	$99.81	8.690%	$108.4835	$108.48	$108.50	$108.50
Purchase #4	$115.56	10.391%	$127.5678	$127.57	$127.55	$127.60
Purchase #5	$227.92	10.503%	$251.8584	$251.86	$251.85	$251.90
Purchase #6	$174.54	4.504%	$182.4013	$182.40	$182.40	$182.40
Purchase #7	$154.66	13.566%	$175.6412	$175.64	$175.65	$175.60
7 purchase totals =	$1,035.70		$1,139.5418	$1,139.54	$1,139.55	$1,139.60