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	$5.61	9.756%	$6.1573	$6.16	$6.15	$6.20
Purchase #2	$37.46	11.472%	$41.7574	$41.76	$41.75	$41.80
Purchase #3	$85.53	4.432%	$89.3207	$89.32	$89.30	$89.30
Purchase #4	$204.33	3.348%	$211.171	$211.17	$211.15	$211.20
Purchase #5	$90.86	10.265%	$100.1868	$100.19	$100.20	$100.20
Purchase #6	$120.27	10.573%	$132.9861	$132.99	$133.00	$133.00
Purchase #7	$79.37	3.132%	$81.8559	$81.86	$81.85	$81.90
7 purchase totals =	$623.43		$663.4352	$663.45	$663.40	$663.60