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	$146.57	7.482%	$157.5364	$157.54	$157.55	$157.50
Purchase #2	$85.56	5.562%	$90.3188	$90.32	$90.30	$90.30
Purchase #3	$234.89	3.392%	$242.8575	$242.86	$242.85	$242.90
Purchase #4	$76.33	6.300%	$81.1388	$81.14	$81.15	$81.10
Purchase #5	$46.49	9.527%	$50.9191	$50.92	$50.90	$50.90
Purchase #6	$138.93	7.165%	$148.8843	$148.88	$148.90	$148.90
Purchase #7	$35.81	13.859%	$40.7729	$40.77	$40.75	$40.80
7 purchase totals =	$764.58		$812.4278	$812.43	$812.40	$812.40