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	$168.90	6.144%	$179.2772	$179.28	$179.30	$179.30
Purchase #2	$195.85	5.199%	$206.0322	$206.03	$206.05	$206.00
Purchase #3	$137.95	8.380%	$149.5102	$149.51	$149.50	$149.50
Purchase #4	$26.31	11.559%	$29.3512	$29.35	$29.35	$29.40
Purchase #5	$173.25	10.773%	$191.9142	$191.91	$191.90	$191.90
Purchase #6	$102.43	9.849%	$112.5183	$112.52	$112.50	$112.50
Purchase #7	$76.61	11.367%	$85.3183	$85.32	$85.30	$85.30
7 purchase totals =	$881.30		$953.9216	$953.92	$953.90	$953.90