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	$161.69	4.104%	$168.3258	$168.33	$168.35	$168.30
Purchase #2	$138.52	3.600%	$143.5067	$143.51	$143.50	$143.50
Purchase #3	$47.91	10.358%	$52.8725	$52.87	$52.85	$52.90
Purchase #4	$85.85	9.810%	$94.2719	$94.27	$94.25	$94.30
Purchase #5	$6.35	13.430%	$7.2028	$7.20	$7.20	$7.20
Purchase #6	$129.99	5.579%	$137.2421	$137.24	$137.25	$137.20
Purchase #7	$85.55	5.572%	$90.3168	$90.32	$90.30	$90.30
7 purchase totals =	$655.86		$693.7386	$693.74	$693.70	$693.70