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	$30.96	6.864%	$33.0851	$33.09	$33.10	$33.10
Purchase #2	$79.38	7.200%	$85.0954	$85.10	$85.10	$85.10
Purchase #3	$104.32	7.342%	$111.9792	$111.98	$112.00	$112.00
Purchase #4	$114.30	5.186%	$120.2276	$120.23	$120.25	$120.20
Purchase #5	$195.46	13.114%	$221.0926	$221.09	$221.10	$221.10
Purchase #6	$33.41	12.555%	$37.6046	$37.60	$37.60	$37.60
Purchase #7	$153.67	11.309%	$171.0485	$171.05	$171.05	$171.00
7 purchase totals =	$711.50		$780.1330	$780.14	$780.20	$780.10