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	$78.47	13.485%	$89.0517	$89.05	$89.05	$89.10
Purchase #2	$94.82	7.825%	$102.2397	$102.24	$102.25	$102.20
Purchase #3	$120.69	6.141%	$128.1016	$128.10	$128.10	$128.10
Purchase #4	$52.34	9.666%	$57.3992	$57.40	$57.40	$57.40
Purchase #5	$131.87	11.339%	$146.8227	$146.82	$146.80	$146.80
Purchase #6	$195.56	7.409%	$210.049	$210.05	$210.05	$210.00
Purchase #7	$156.83	3.235%	$161.9035	$161.90	$161.90	$161.90
7 purchase totals =	$830.58		$895.5674	$895.56	$895.55	$895.50