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	$235.88	6.300%	$250.7404	$250.74	$250.75	$250.70
Purchase #2	$91.97	8.270%	$99.5759	$99.58	$99.60	$99.60
Purchase #3	$40.93	6.341%	$43.5254	$43.53	$43.55	$43.50
Purchase #4	$132.26	8.504%	$143.5074	$143.51	$143.50	$143.50
Purchase #5	$117.37	10.242%	$129.391	$129.39	$129.40	$129.40
Purchase #6	$55.76	13.639%	$63.3651	$63.37	$63.35	$63.40
Purchase #7	$150.79	11.679%	$168.4008	$168.40	$168.40	$168.40
7 purchase totals =	$824.96		$898.5060	$898.52	$898.55	$898.50