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	$145.34	4.154%	$151.3774	$151.38	$151.40	$151.40
Purchase #2	$180.37	12.488%	$202.8946	$202.89	$202.90	$202.90
Purchase #3	$83.92	6.642%	$89.494	$89.49	$89.50	$89.50
Purchase #4	$91.51	13.736%	$104.0798	$104.08	$104.10	$104.10
Purchase #5	$115.25	10.666%	$127.5426	$127.54	$127.55	$127.50
Purchase #6	$174.57	8.696%	$189.7506	$189.75	$189.75	$189.80
Purchase #7	$30.74	12.663%	$34.6326	$34.63	$34.65	$34.60
7 purchase totals =	$821.70		$899.7716	$899.76	$899.85	$899.80