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	$244.83	12.234%	$274.7825	$274.78	$274.80	$274.80
Purchase #2	$200.25	11.215%	$222.708	$222.71	$222.70	$222.70
Purchase #3	$247.45	9.694%	$271.4378	$271.44	$271.45	$271.40
Purchase #4	$69.91	12.228%	$78.4586	$78.46	$78.45	$78.50
Purchase #5	$126.33	4.412%	$131.9037	$131.90	$131.90	$131.90
Purchase #6	$92.56	6.342%	$98.4302	$98.43	$98.45	$98.40
Purchase #7	$57.95	8.155%	$62.6758	$62.68	$62.70	$62.70
7 purchase totals =	$1,039.28		$1,140.3966	$1,140.40	$1,140.45	$1,140.40