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	$39.86	4.274%	$41.5636	$41.56	$41.55	$41.60
Purchase #2	$127.63	3.569%	$132.1851	$132.19	$132.20	$132.20
Purchase #3	$188.72	11.541%	$210.5002	$210.50	$210.50	$210.50
Purchase #4	$128.37	11.164%	$142.7012	$142.70	$142.70	$142.70
Purchase #5	$43.34	12.458%	$48.7393	$48.74	$48.75	$48.70
Purchase #6	$222.81	13.663%	$253.2525	$253.25	$253.25	$253.30
Purchase #7	$146.45	12.315%	$164.4853	$164.49	$164.50	$164.50
7 purchase totals =	$897.18		$993.4272	$993.43	$993.45	$993.50