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	$39.94	13.168%	$45.1993	$45.20	$45.20	$45.20
Purchase #2	$159.87	11.785%	$178.7107	$178.71	$178.70	$178.70
Purchase #3	$20.74	4.275%	$21.6266	$21.63	$21.65	$21.60
Purchase #4	$67.73	7.172%	$72.5876	$72.59	$72.60	$72.60
Purchase #5	$102.29	12.631%	$115.2102	$115.21	$115.20	$115.20
Purchase #6	$119.70	5.539%	$126.3302	$126.33	$126.35	$126.30
Purchase #7	$162.46	11.746%	$181.5426	$181.54	$181.55	$181.50
7 purchase totals =	$672.73		$741.2072	$741.21	$741.25	$741.10