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	$52.63	6.621%	$56.1146	$56.11	$56.10	$56.10
Purchase #2	$246.37	13.155%	$278.78	$278.78	$278.80	$278.80
Purchase #3	$49.83	9.531%	$54.5793	$54.58	$54.60	$54.60
Purchase #4	$243.43	8.359%	$263.7783	$263.78	$263.80	$263.80
Purchase #5	$190.41	9.848%	$209.1616	$209.16	$209.15	$209.20
Purchase #6	$31.79	11.863%	$35.5612	$35.56	$35.55	$35.60
Purchase #7	$72.65	8.395%	$78.749	$78.75	$78.75	$78.70
7 purchase totals =	$887.11		$976.7240	$976.72	$976.75	$976.80