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	$83.71	8.133%	$90.5181	$90.52	$90.50	$90.50
Purchase #2	$181.62	4.592%	$189.96	$189.96	$189.95	$190.00
Purchase #3	$74.32	12.293%	$83.4562	$83.46	$83.45	$83.50
Purchase #4	$134.49	13.261%	$152.3247	$152.32	$152.30	$152.30
Purchase #5	$138.83	11.400%	$154.6566	$154.66	$154.65	$154.70
Purchase #6	$107.50	3.129%	$110.8637	$110.86	$110.85	$110.90
Purchase #7	$203.25	3.783%	$210.9389	$210.94	$210.95	$210.90
7 purchase totals =	$923.72		$992.7182	$992.72	$992.65	$992.80