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	$151.54	9.336%	$165.6878	$165.69	$165.70	$165.70
Purchase #2	$39.72	7.751%	$42.7987	$42.80	$42.80	$42.80
Purchase #3	$169.74	11.568%	$189.3755	$189.38	$189.40	$189.40
Purchase #4	$68.71	4.544%	$71.8322	$71.83	$71.85	$71.80
Purchase #5	$215.47	5.828%	$228.0276	$228.03	$228.05	$228.00
Purchase #6	$59.38	8.714%	$64.5544	$64.55	$64.55	$64.60
Purchase #7	$61.76	9.444%	$67.5926	$67.59	$67.60	$67.60
7 purchase totals =	$766.32		$829.8688	$829.87	$829.95	$829.90