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	$46.72	8.869%	$50.8636	$50.86	$50.85	$50.90
Purchase #2	$24.78	4.599%	$25.9196	$25.92	$25.90	$25.90
Purchase #3	$89.34	6.145%	$94.8299	$94.83	$94.85	$94.80
Purchase #4	$57.57	5.336%	$60.6419	$60.64	$60.65	$60.60
Purchase #5	$142.79	4.132%	$148.6901	$148.69	$148.70	$148.70
Purchase #6	$119.74	4.711%	$125.381	$125.38	$125.40	$125.40
Purchase #7	$39.78	13.162%	$45.0158	$45.02	$45.00	$45.00
7 purchase totals =	$520.72		$551.3419	$551.34	$551.35	$551.30