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	$42.54	11.578%	$47.4653	$47.47	$47.45	$47.50
Purchase #2	$188.42	10.648%	$208.483	$208.48	$208.50	$208.50
Purchase #3	$170.33	10.543%	$188.2879	$188.29	$188.30	$188.30
Purchase #4	$104.69	12.447%	$117.7208	$117.72	$117.70	$117.70
Purchase #5	$28.53	10.487%	$31.5219	$31.52	$31.50	$31.50
Purchase #6	$54.53	13.730%	$62.017	$62.02	$62.00	$62.00
Purchase #7	$103.31	7.211%	$110.7597	$110.76	$110.75	$110.80
7 purchase totals =	$692.35		$766.2556	$766.26	$766.20	$766.30