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	$172.66	13.674%	$196.2695	$196.27	$196.25	$196.30
Purchase #2	$131.78	9.447%	$144.2293	$144.23	$144.25	$144.20
Purchase #3	$248.38	8.780%	$270.1878	$270.19	$270.20	$270.20
Purchase #4	$80.87	10.293%	$89.1939	$89.19	$89.20	$89.20
Purchase #5	$72.62	10.858%	$80.5051	$80.51	$80.50	$80.50
Purchase #6	$53.55	13.519%	$60.7894	$60.79	$60.80	$60.80
Purchase #7	$136.63	11.172%	$151.8943	$151.89	$151.90	$151.90
7 purchase totals =	$896.49		$993.0693	$993.07	$993.10	$993.10