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	$203.73	12.109%	$228.3997	$228.40	$228.40	$228.40
Purchase #2	$12.27	8.583%	$13.3231	$13.32	$13.30	$13.30
Purchase #3	$37.74	10.436%	$41.6785	$41.68	$41.70	$41.70
Purchase #4	$93.67	5.507%	$98.8284	$98.83	$98.85	$98.80
Purchase #5	$160.32	7.498%	$172.3408	$172.34	$172.35	$172.30
Purchase #6	$53.39	10.718%	$59.1123	$59.11	$59.10	$59.10
Purchase #7	$122.43	3.836%	$127.1264	$127.13	$127.15	$127.10
7 purchase totals =	$683.55		$740.8092	$740.81	$740.85	$740.70