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	$93.58	6.394%	$99.5635	$99.56	$99.55	$99.60
Purchase #2	$249.27	10.526%	$275.5082	$275.51	$275.50	$275.50
Purchase #3	$24.50	5.151%	$25.762	$25.76	$25.75	$25.80
Purchase #4	$118.77	10.363%	$131.0781	$131.08	$131.10	$131.10
Purchase #5	$245.69	12.454%	$276.2882	$276.29	$276.30	$276.30
Purchase #6	$159.58	10.413%	$176.1971	$176.20	$176.20	$176.20
Purchase #7	$31.83	13.420%	$36.1016	$36.10	$36.10	$36.10
7 purchase totals =	$923.22		$1,020.4987	$1,020.50	$1,020.50	$1,020.60