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	$75.34	3.234%	$77.7765	$77.78	$77.80	$77.80
Purchase #2	$86.39	4.756%	$90.4987	$90.50	$90.50	$90.50
Purchase #3	$57.86	11.331%	$64.4161	$64.42	$64.40	$64.40
Purchase #4	$158.90	12.546%	$178.8356	$178.84	$178.85	$178.80
Purchase #5	$63.92	11.831%	$71.4824	$71.48	$71.50	$71.50
Purchase #6	$25.43	5.402%	$26.8037	$26.80	$26.80	$26.80
Purchase #7	$67.29	10.854%	$74.5937	$74.59	$74.60	$74.60
7 purchase totals =	$535.13		$584.4067	$584.41	$584.45	$584.40