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	$235.91	6.183%	$250.4963	$250.50	$250.50	$250.50
Purchase #2	$182.91	7.673%	$196.9447	$196.94	$196.95	$196.90
Purchase #3	$208.42	7.390%	$223.8222	$223.82	$223.80	$223.80
Purchase #4	$56.32	13.843%	$64.1164	$64.12	$64.10	$64.10
Purchase #5	$170.93	13.440%	$193.903	$193.90	$193.90	$193.90
Purchase #6	$28.49	10.343%	$31.4367	$31.44	$31.45	$31.40
Purchase #7	$34.62	5.404%	$36.4909	$36.49	$36.50	$36.50
7 purchase totals =	$917.60		$997.2102	$997.21	$997.20	$997.10