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	$11.63	13.657%	$13.2183	$13.22	$13.20	$13.20
Purchase #2	$200.55	11.140%	$222.8913	$222.89	$222.90	$222.90
Purchase #3	$61.74	9.524%	$67.6201	$67.62	$67.60	$67.60
Purchase #4	$105.89	7.464%	$113.7936	$113.79	$113.80	$113.80
Purchase #5	$58.91	9.141%	$64.295	$64.30	$64.30	$64.30
Purchase #6	$177.47	8.648%	$192.8176	$192.82	$192.80	$192.80
Purchase #7	$11.64	5.853%	$12.3213	$12.32	$12.30	$12.30
7 purchase totals =	$627.83		$686.9572	$686.96	$686.90	$686.90