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	$206.67	6.165%	$219.4112	$219.41	$219.40	$219.40
Purchase #2	$38.64	11.580%	$43.1145	$43.11	$43.10	$43.10
Purchase #3	$86.75	5.758%	$91.7451	$91.75	$91.75	$91.70
Purchase #4	$149.44	10.643%	$165.3449	$165.34	$165.35	$165.30
Purchase #5	$175.94	11.564%	$196.2857	$196.29	$196.30	$196.30
Purchase #6	$75.45	4.816%	$79.0837	$79.08	$79.10	$79.10
Purchase #7	$99.62	13.318%	$112.8874	$112.89	$112.90	$112.90
7 purchase totals =	$832.51		$907.8725	$907.87	$907.90	$907.80