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	$228.29	9.592%	$250.1876	$250.19	$250.20	$250.20
Purchase #2	$73.69	11.675%	$82.2933	$82.29	$82.30	$82.30
Purchase #3	$142.43	12.701%	$160.52	$160.52	$160.50	$160.50
Purchase #4	$152.65	13.446%	$173.1753	$173.18	$173.20	$173.20
Purchase #5	$232.54	13.741%	$264.4933	$264.49	$264.50	$264.50
Purchase #6	$45.61	12.174%	$51.1626	$51.16	$51.15	$51.20
Purchase #7	$67.90	9.588%	$74.4103	$74.41	$74.40	$74.40
7 purchase totals =	$943.11		$1,056.2424	$1,056.24	$1,056.25	$1,056.30