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	$134.38	6.252%	$142.7814	$142.78	$142.80	$142.80
Purchase #2	$56.54	6.259%	$60.0788	$60.08	$60.10	$60.10
Purchase #3	$36.48	12.500%	$41.04	$41.04	$41.05	$41.00
Purchase #4	$87.51	13.352%	$99.1943	$99.19	$99.20	$99.20
Purchase #5	$247.50	11.260%	$275.3685	$275.37	$275.35	$275.40
Purchase #6	$93.73	11.102%	$104.1359	$104.14	$104.15	$104.10
Purchase #7	$161.94	12.116%	$181.5607	$181.56	$181.55	$181.60
7 purchase totals =	$818.08		$904.1596	$904.16	$904.20	$904.20