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	$188.88	6.400%	$200.9683	$200.97	$200.95	$201.00
Purchase #2	$27.38	7.601%	$29.4612	$29.46	$29.45	$29.50
Purchase #3	$36.56	10.150%	$40.2708	$40.27	$40.25	$40.30
Purchase #4	$26.45	10.497%	$29.2265	$29.23	$29.25	$29.20
Purchase #5	$136.47	6.173%	$144.8943	$144.89	$144.90	$144.90
Purchase #6	$108.53	12.697%	$122.3101	$122.31	$122.30	$122.30
Purchase #7	$93.27	3.195%	$96.25	$96.25	$96.25	$96.30
7 purchase totals =	$617.54		$663.3812	$663.38	$663.35	$663.50