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	$190.68	6.472%	$203.0208	$203.02	$203.00	$203.00
Purchase #2	$206.86	7.561%	$222.5007	$222.50	$222.50	$222.50
Purchase #3	$75.58	10.832%	$83.7668	$83.77	$83.75	$83.80
Purchase #4	$119.48	12.647%	$134.5906	$134.59	$134.60	$134.60
Purchase #5	$109.69	8.143%	$118.6221	$118.62	$118.60	$118.60
Purchase #6	$56.70	5.405%	$59.7646	$59.76	$59.75	$59.80
Purchase #7	$78.68	8.824%	$85.6227	$85.62	$85.60	$85.60
7 purchase totals =	$837.67		$907.8883	$907.88	$907.80	$907.90