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	$71.89	10.295%	$79.2911	$79.29	$79.30	$79.30
Purchase #2	$67.34	5.715%	$71.1885	$71.19	$71.20	$71.20
Purchase #3	$51.48	10.570%	$56.9214	$56.92	$56.90	$56.90
Purchase #4	$84.76	5.498%	$89.4201	$89.42	$89.40	$89.40
Purchase #5	$7.81	3.509%	$8.0841	$8.08	$8.10	$8.10
Purchase #6	$227.83	12.746%	$256.8692	$256.87	$256.85	$256.90
Purchase #7	$166.96	11.577%	$186.289	$186.29	$186.30	$186.30
7 purchase totals =	$678.07		$748.0634	$748.06	$748.05	$748.10