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	$227.79	10.800%	$252.3913	$252.39	$252.40	$252.40
Purchase #2	$191.30	8.845%	$208.2205	$208.22	$208.20	$208.20
Purchase #3	$239.56	6.673%	$255.5458	$255.55	$255.55	$255.50
Purchase #4	$108.38	11.510%	$120.8545	$120.85	$120.85	$120.90
Purchase #5	$82.79	4.150%	$86.2258	$86.23	$86.25	$86.20
Purchase #6	$152.33	12.342%	$171.1306	$171.13	$171.15	$171.10
Purchase #7	$159.46	12.659%	$179.646	$179.65	$179.65	$179.60
7 purchase totals =	$1,161.61		$1,274.0145	$1,274.02	$1,274.05	$1,273.90