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	$63.82	5.204%	$67.1412	$67.14	$67.15	$67.10
Purchase #2	$249.81	9.605%	$273.8043	$273.80	$273.80	$273.80
Purchase #3	$180.56	7.460%	$194.0298	$194.03	$194.05	$194.00
Purchase #4	$55.37	11.784%	$61.8948	$61.89	$61.90	$61.90
Purchase #5	$179.85	5.668%	$190.0439	$190.04	$190.05	$190.00
Purchase #6	$238.46	10.873%	$264.3878	$264.39	$264.40	$264.40
Purchase #7	$59.69	11.861%	$66.7698	$66.77	$66.75	$66.80
7 purchase totals =	$1,027.56		$1,118.0716	$1,118.06	$1,118.10	$1,118.00