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	$233.44	7.137%	$250.1006	$250.10	$250.10	$250.10
Purchase #2	$132.58	7.795%	$142.9146	$142.91	$142.90	$142.90
Purchase #3	$152.96	7.422%	$164.3127	$164.31	$164.30	$164.30
Purchase #4	$32.38	3.406%	$33.4829	$33.48	$33.50	$33.50
Purchase #5	$11.95	12.395%	$13.4312	$13.43	$13.45	$13.40
Purchase #6	$153.61	7.761%	$165.5317	$165.53	$165.55	$165.50
Purchase #7	$229.41	9.108%	$250.3047	$250.30	$250.30	$250.30
7 purchase totals =	$946.33		$1,020.0784	$1,020.06	$1,020.10	$1,020.00