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	$27.79	3.706%	$28.8199	$28.82	$28.80	$28.80
Purchase #2	$138.35	6.155%	$146.8654	$146.87	$146.85	$146.90
Purchase #3	$90.33	3.791%	$93.7544	$93.75	$93.75	$93.80
Purchase #4	$158.82	12.637%	$178.8901	$178.89	$178.90	$178.90
Purchase #5	$59.85	13.426%	$67.8855	$67.89	$67.90	$67.90
Purchase #6	$73.48	13.291%	$83.2462	$83.25	$83.25	$83.20
Purchase #7	$126.33	9.568%	$138.4173	$138.42	$138.40	$138.40
7 purchase totals =	$674.95		$737.8788	$737.89	$737.85	$737.90