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	$138.89	4.679%	$145.3887	$145.39	$145.40	$145.40
Purchase #2	$200.92	13.738%	$228.5224	$228.52	$228.50	$228.50
Purchase #3	$198.79	6.408%	$211.5285	$211.53	$211.55	$211.50
Purchase #4	$78.68	8.365%	$85.2616	$85.26	$85.25	$85.30
Purchase #5	$79.93	11.755%	$89.3258	$89.33	$89.35	$89.30
Purchase #6	$86.40	3.556%	$89.4724	$89.47	$89.45	$89.50
Purchase #7	$36.88	8.183%	$39.8979	$39.90	$39.90	$39.90
7 purchase totals =	$820.49		$889.3973	$889.40	$889.40	$889.40