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	$25.90	9.252%	$28.2963	$28.30	$28.30	$28.30
Purchase #2	$60.86	6.518%	$64.8269	$64.83	$64.85	$64.80
Purchase #3	$143.56	6.235%	$152.511	$152.51	$152.50	$152.50
Purchase #4	$88.34	6.460%	$94.0468	$94.05	$94.05	$94.00
Purchase #5	$137.44	3.630%	$142.4291	$142.43	$142.45	$142.40
Purchase #6	$199.74	13.798%	$227.3001	$227.30	$227.30	$227.30
Purchase #7	$99.99	11.119%	$111.1079	$111.11	$111.10	$111.10
7 purchase totals =	$755.83		$820.5181	$820.53	$820.55	$820.40