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	$87.58	9.697%	$96.0726	$96.07	$96.05	$96.10
Purchase #2	$35.88	7.122%	$38.4354	$38.44	$38.45	$38.40
Purchase #3	$67.71	5.539%	$71.4605	$71.46	$71.45	$71.50
Purchase #4	$36.56	6.424%	$38.9086	$38.91	$38.90	$38.90
Purchase #5	$139.28	10.862%	$154.4086	$154.41	$154.40	$154.40
Purchase #6	$31.70	6.213%	$33.6695	$33.67	$33.65	$33.70
Purchase #7	$191.94	8.611%	$208.468	$208.47	$208.45	$208.50
7 purchase totals =	$590.65		$641.4232	$641.43	$641.35	$641.50