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	$195.66	12.290%	$219.7066	$219.71	$219.70	$219.70
Purchase #2	$47.64	9.634%	$52.2296	$52.23	$52.25	$52.20
Purchase #3	$166.51	8.599%	$180.8282	$180.83	$180.85	$180.80
Purchase #4	$96.94	3.659%	$100.487	$100.49	$100.50	$100.50
Purchase #5	$57.84	11.208%	$64.3227	$64.32	$64.30	$64.30
Purchase #6	$94.31	9.742%	$103.4977	$103.50	$103.50	$103.50
Purchase #7	$221.49	3.631%	$229.5323	$229.53	$229.55	$229.50
7 purchase totals =	$880.39		$950.6041	$950.61	$950.65	$950.50