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	$127.34	3.277%	$131.5129	$131.51	$131.50	$131.50
Purchase #2	$38.75	8.233%	$41.9403	$41.94	$41.95	$41.90
Purchase #3	$108.61	7.819%	$117.1022	$117.10	$117.10	$117.10
Purchase #4	$99.78	5.568%	$105.3358	$105.34	$105.35	$105.30
Purchase #5	$26.48	13.449%	$30.0413	$30.04	$30.05	$30.00
Purchase #6	$100.86	12.340%	$113.3061	$113.31	$113.30	$113.30
Purchase #7	$244.63	10.131%	$269.4135	$269.41	$269.40	$269.40
7 purchase totals =	$746.45		$808.6521	$808.65	$808.65	$808.50