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	$13.90	4.735%	$14.5582	$14.56	$14.55	$14.60
Purchase #2	$67.82	8.842%	$73.8166	$73.82	$73.80	$73.80
Purchase #3	$61.88	13.400%	$70.1719	$70.17	$70.15	$70.20
Purchase #4	$81.52	8.564%	$88.5014	$88.50	$88.50	$88.50
Purchase #5	$131.52	6.349%	$139.8702	$139.87	$139.85	$139.90
Purchase #6	$117.86	8.369%	$127.7237	$127.72	$127.70	$127.70
Purchase #7	$120.43	4.514%	$125.8662	$125.87	$125.85	$125.90
7 purchase totals =	$594.93		$640.5082	$640.51	$640.40	$640.60