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	$136.58	5.331%	$143.8611	$143.86	$143.85	$143.90
Purchase #2	$125.98	13.143%	$142.5376	$142.54	$142.55	$142.50
Purchase #3	$91.25	13.361%	$103.4419	$103.44	$103.45	$103.40
Purchase #4	$200.62	11.123%	$222.935	$222.94	$222.95	$222.90
Purchase #5	$142.72	11.746%	$159.4839	$159.48	$159.50	$159.50
Purchase #6	$127.70	3.296%	$131.909	$131.91	$131.90	$131.90
Purchase #7	$66.79	3.465%	$69.1043	$69.10	$69.10	$69.10
7 purchase totals =	$891.64		$973.2728	$973.27	$973.30	$973.20