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	$85.88	4.434%	$89.6879	$89.69	$89.70	$89.70
Purchase #2	$149.85	11.665%	$167.33	$167.33	$167.35	$167.30
Purchase #3	$83.40	9.494%	$91.318	$91.32	$91.30	$91.30
Purchase #4	$51.76	7.466%	$55.6244	$55.62	$55.60	$55.60
Purchase #5	$44.40	6.187%	$47.147	$47.15	$47.15	$47.10
Purchase #6	$115.39	12.865%	$130.2349	$130.23	$130.25	$130.20
Purchase #7	$124.54	4.438%	$130.0671	$130.07	$130.05	$130.10
7 purchase totals =	$655.22		$711.4093	$711.41	$711.40	$711.30