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	$168.83	12.647%	$190.1819	$190.18	$190.20	$190.20
Purchase #2	$101.89	3.252%	$105.2035	$105.20	$105.20	$105.20
Purchase #3	$98.29	5.533%	$103.7284	$103.73	$103.75	$103.70
Purchase #4	$84.96	11.206%	$94.4806	$94.48	$94.50	$94.50
Purchase #5	$121.82	3.818%	$126.4711	$126.47	$126.45	$126.50
Purchase #6	$177.43	4.781%	$185.9129	$185.91	$185.90	$185.90
Purchase #7	$126.56	13.563%	$143.7253	$143.73	$143.75	$143.70
7 purchase totals =	$879.78		$949.7037	$949.70	$949.75	$949.70