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	$42.53	7.544%	$45.7385	$45.74	$45.75	$45.70
Purchase #2	$106.49	6.489%	$113.4001	$113.40	$113.40	$113.40
Purchase #3	$28.57	11.440%	$31.8384	$31.84	$31.85	$31.80
Purchase #4	$215.64	13.459%	$244.663	$244.66	$244.65	$244.70
Purchase #5	$52.64	7.204%	$56.4322	$56.43	$56.45	$56.40
Purchase #6	$109.47	8.459%	$118.7301	$118.73	$118.75	$118.70
Purchase #7	$51.43	7.321%	$55.1952	$55.20	$55.20	$55.20
7 purchase totals =	$606.77		$665.9975	$666.00	$666.05	$665.90