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	$84.54	6.722%	$90.2228	$90.22	$90.20	$90.20
Purchase #2	$28.45	5.652%	$30.058	$30.06	$30.05	$30.10
Purchase #3	$91.49	7.586%	$98.4304	$98.43	$98.45	$98.40
Purchase #4	$124.64	11.800%	$139.3475	$139.35	$139.35	$139.30
Purchase #5	$131.98	7.658%	$142.087	$142.09	$142.10	$142.10
Purchase #6	$67.59	7.182%	$72.4443	$72.44	$72.45	$72.40
Purchase #7	$9.74	5.633%	$10.2887	$10.29	$10.30	$10.30
7 purchase totals =	$538.43		$582.8787	$582.88	$582.90	$582.80