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	$50.29	8.757%	$54.6939	$54.69	$54.70	$54.70
Purchase #2	$187.84	12.278%	$210.903	$210.90	$210.90	$210.90
Purchase #3	$91.70	9.853%	$100.7352	$100.74	$100.75	$100.70
Purchase #4	$131.77	6.828%	$140.7673	$140.77	$140.75	$140.80
Purchase #5	$21.28	7.519%	$22.88	$22.88	$22.90	$22.90
Purchase #6	$74.61	13.270%	$84.5107	$84.51	$84.50	$84.50
Purchase #7	$86.30	4.166%	$89.8953	$89.90	$89.90	$89.90
7 purchase totals =	$643.79		$704.3854	$704.39	$704.40	$704.40