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	$17.72	13.726%	$20.1522	$20.15	$20.15	$20.20
Purchase #2	$208.46	12.220%	$233.9338	$233.93	$233.95	$233.90
Purchase #3	$18.95	9.700%	$20.7882	$20.79	$20.80	$20.80
Purchase #4	$41.79	9.746%	$45.8629	$45.86	$45.85	$45.90
Purchase #5	$36.78	9.658%	$40.3322	$40.33	$40.35	$40.30
Purchase #6	$195.72	9.367%	$214.0531	$214.05	$214.05	$214.10
Purchase #7	$165.71	11.410%	$184.6175	$184.62	$184.60	$184.60
7 purchase totals =	$685.13		$759.7399	$759.73	$759.75	$759.80