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	$168.53	6.154%	$178.9013	$178.90	$178.90	$178.90
Purchase #2	$190.34	4.415%	$198.7435	$198.74	$198.75	$198.70
Purchase #3	$110.39	12.747%	$124.4614	$124.46	$124.45	$124.50
Purchase #4	$109.43	12.836%	$123.4764	$123.48	$123.50	$123.50
Purchase #5	$133.49	13.143%	$151.0346	$151.03	$151.05	$151.00
Purchase #6	$111.94	11.248%	$124.531	$124.53	$124.55	$124.50
Purchase #7	$6.37	13.733%	$7.2448	$7.24	$7.25	$7.20
7 purchase totals =	$830.49		$908.3930	$908.38	$908.45	$908.30