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	$246.52	3.240%	$254.5072	$254.51	$254.50	$254.50
Purchase #2	$113.60	12.251%	$127.5171	$127.52	$127.50	$127.50
Purchase #3	$20.48	8.537%	$22.2284	$22.23	$22.25	$22.20
Purchase #4	$118.44	6.264%	$125.8591	$125.86	$125.85	$125.90
Purchase #5	$237.88	7.691%	$256.1754	$256.18	$256.20	$256.20
Purchase #6	$16.65	13.662%	$18.9247	$18.92	$18.90	$18.90
Purchase #7	$142.59	5.549%	$150.5023	$150.50	$150.50	$150.50
7 purchase totals =	$896.16		$955.7142	$955.72	$955.70	$955.70