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	$126.77	12.412%	$142.5047	$142.50	$142.50	$142.50
Purchase #2	$233.55	12.651%	$263.0964	$263.10	$263.10	$263.10
Purchase #3	$99.49	9.375%	$108.8172	$108.82	$108.80	$108.80
Purchase #4	$80.72	10.292%	$89.0277	$89.03	$89.05	$89.00
Purchase #5	$57.40	3.659%	$59.5003	$59.50	$59.50	$59.50
Purchase #6	$7.46	12.722%	$8.4091	$8.41	$8.40	$8.40
Purchase #7	$183.30	4.121%	$190.8538	$190.85	$190.85	$190.90
7 purchase totals =	$788.69		$862.2092	$862.21	$862.20	$862.20