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	$31.87	5.734%	$33.6974	$33.70	$33.70	$33.70
Purchase #2	$43.42	10.203%	$47.8501	$47.85	$47.85	$47.90
Purchase #3	$198.48	8.634%	$215.6168	$215.62	$215.60	$215.60
Purchase #4	$40.35	5.108%	$42.4111	$42.41	$42.40	$42.40
Purchase #5	$61.62	5.297%	$64.884	$64.88	$64.90	$64.90
Purchase #6	$78.44	3.775%	$81.4011	$81.40	$81.40	$81.40
Purchase #7	$62.28	7.436%	$66.9111	$66.91	$66.90	$66.90
7 purchase totals =	$516.46		$552.7716	$552.77	$552.75	$552.80