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	$250.89	13.722%	$285.3171	$285.32	$285.30	$285.30
Purchase #2	$46.82	10.811%	$51.8817	$51.88	$51.90	$51.90
Purchase #3	$244.84	11.790%	$273.7066	$273.71	$273.70	$273.70
Purchase #4	$82.70	7.824%	$89.1704	$89.17	$89.15	$89.20
Purchase #5	$16.84	8.710%	$18.3068	$18.31	$18.30	$18.30
Purchase #6	$51.73	3.732%	$53.6606	$53.66	$53.65	$53.70
Purchase #7	$90.74	11.584%	$101.2513	$101.25	$101.25	$101.30
7 purchase totals =	$784.56		$873.2945	$873.30	$873.25	$873.40