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	$108.46	6.740%	$115.7702	$115.77	$115.75	$115.80
Purchase #2	$46.72	10.164%	$51.4686	$51.47	$51.45	$51.50
Purchase #3	$52.79	5.231%	$55.5514	$55.55	$55.55	$55.60
Purchase #4	$29.73	10.711%	$32.9144	$32.91	$32.90	$32.90
Purchase #5	$62.49	8.522%	$67.8154	$67.82	$67.80	$67.80
Purchase #6	$147.41	5.779%	$155.9288	$155.93	$155.95	$155.90
Purchase #7	$102.77	8.342%	$111.3431	$111.34	$111.35	$111.30
7 purchase totals =	$550.37		$590.7919	$590.79	$590.75	$590.80