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	$49.72	13.120%	$56.2433	$56.24	$56.25	$56.20
Purchase #2	$51.35	6.757%	$54.8197	$54.82	$54.80	$54.80
Purchase #3	$93.25	9.148%	$101.7805	$101.78	$101.80	$101.80
Purchase #4	$31.35	13.444%	$35.5647	$35.56	$35.55	$35.60
Purchase #5	$120.36	13.427%	$136.5207	$136.52	$136.50	$136.50
Purchase #6	$87.63	6.680%	$93.4837	$93.48	$93.50	$93.50
Purchase #7	$37.25	13.753%	$42.373	$42.37	$42.35	$42.40
7 purchase totals =	$470.91		$520.7856	$520.77	$520.75	$520.80