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	$113.86	12.322%	$127.8898	$127.89	$127.90	$127.90
Purchase #2	$134.63	4.541%	$140.7435	$140.74	$140.75	$140.70
Purchase #3	$88.53	11.485%	$98.6977	$98.70	$98.70	$98.70
Purchase #4	$64.96	10.756%	$71.9471	$71.95	$71.95	$71.90
Purchase #5	$52.49	8.785%	$57.1012	$57.10	$57.10	$57.10
Purchase #6	$112.70	12.229%	$126.4821	$126.48	$126.50	$126.50
Purchase #7	$31.32	3.702%	$32.4795	$32.48	$32.50	$32.50
7 purchase totals =	$598.49		$655.3409	$655.34	$655.40	$655.30