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	$73.56	13.579%	$83.5487	$83.55	$83.55	$83.50
Purchase #2	$170.95	6.729%	$182.4532	$182.45	$182.45	$182.50
Purchase #3	$91.83	6.632%	$97.9202	$97.92	$97.90	$97.90
Purchase #4	$19.39	4.637%	$20.2891	$20.29	$20.30	$20.30
Purchase #5	$145.48	4.319%	$151.7633	$151.76	$151.75	$151.80
Purchase #6	$95.40	3.260%	$98.51	$98.51	$98.50	$98.50
Purchase #7	$247.26	4.444%	$258.2482	$258.25	$258.25	$258.20
7 purchase totals =	$843.87		$892.7327	$892.73	$892.70	$892.70