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	$60.86	5.326%	$64.1014	$64.10	$64.10	$64.10
Purchase #2	$131.76	5.738%	$139.3204	$139.32	$139.30	$139.30
Purchase #3	$214.59	3.837%	$222.8238	$222.82	$222.80	$222.80
Purchase #4	$95.61	3.359%	$98.8215	$98.82	$98.80	$98.80
Purchase #5	$173.62	9.628%	$190.3361	$190.34	$190.35	$190.30
Purchase #6	$129.79	12.430%	$145.9229	$145.92	$145.90	$145.90
Purchase #7	$60.51	9.597%	$66.3171	$66.32	$66.30	$66.30
7 purchase totals =	$866.74		$927.6432	$927.64	$927.55	$927.50