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	$83.45	4.869%	$87.5132	$87.51	$87.50	$87.50
Purchase #2	$94.89	13.720%	$107.9089	$107.91	$107.90	$107.90
Purchase #3	$240.77	4.353%	$251.2507	$251.25	$251.25	$251.30
Purchase #4	$243.79	12.398%	$274.0151	$274.02	$274.00	$274.00
Purchase #5	$123.38	5.667%	$130.3719	$130.37	$130.35	$130.40
Purchase #6	$88.28	13.213%	$99.9444	$99.94	$99.95	$99.90
Purchase #7	$174.75	12.712%	$196.9642	$196.96	$196.95	$197.00
7 purchase totals =	$1,049.31		$1,147.9684	$1,147.96	$1,147.90	$1,148.00