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	$49.67	3.740%	$51.5277	$51.53	$51.55	$51.50
Purchase #2	$160.38	6.539%	$170.8672	$170.87	$170.85	$170.90
Purchase #3	$33.76	12.473%	$37.9709	$37.97	$37.95	$38.00
Purchase #4	$187.88	4.473%	$196.2839	$196.28	$196.30	$196.30
Purchase #5	$212.41	10.649%	$235.0295	$235.03	$235.05	$235.00
Purchase #6	$55.93	10.193%	$61.6309	$61.63	$61.65	$61.60
Purchase #7	$96.54	3.626%	$100.0405	$100.04	$100.05	$100.00
7 purchase totals =	$796.57		$853.3506	$853.35	$853.40	$853.30