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	$119.36	6.380%	$126.9752	$126.98	$127.00	$127.00
Purchase #2	$89.55	5.170%	$94.1797	$94.18	$94.20	$94.20
Purchase #3	$130.78	12.753%	$147.4584	$147.46	$147.45	$147.50
Purchase #4	$77.72	10.531%	$85.9047	$85.90	$85.90	$85.90
Purchase #5	$47.25	6.298%	$50.2258	$50.23	$50.25	$50.20
Purchase #6	$226.67	12.817%	$255.7223	$255.72	$255.70	$255.70
Purchase #7	$103.88	4.665%	$108.726	$108.73	$108.75	$108.70
7 purchase totals =	$795.21		$869.1921	$869.20	$869.25	$869.20