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	$247.66	12.197%	$277.8671	$277.87	$277.85	$277.90
Purchase #2	$241.40	11.369%	$268.8448	$268.84	$268.85	$268.80
Purchase #3	$109.34	12.592%	$123.1081	$123.11	$123.10	$123.10
Purchase #4	$156.53	5.836%	$165.6651	$165.67	$165.65	$165.70
Purchase #5	$133.55	4.741%	$139.8816	$139.88	$139.90	$139.90
Purchase #6	$233.77	13.337%	$264.9479	$264.95	$264.95	$264.90
Purchase #7	$157.67	8.457%	$171.0042	$171.00	$171.00	$171.00
7 purchase totals =	$1,279.92		$1,411.3188	$1,411.32	$1,411.30	$1,411.30