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	$133.35	3.141%	$137.5385	$137.54	$137.55	$137.50
Purchase #2	$207.33	3.781%	$215.1691	$215.17	$215.15	$215.20
Purchase #3	$99.96	5.254%	$105.2119	$105.21	$105.20	$105.20
Purchase #4	$208.43	7.166%	$223.3661	$223.37	$223.35	$223.40
Purchase #5	$220.54	4.255%	$229.924	$229.92	$229.90	$229.90
Purchase #6	$5.25	10.532%	$5.8029	$5.80	$5.80	$5.80
Purchase #7	$125.32	6.427%	$133.3743	$133.37	$133.35	$133.40
7 purchase totals =	$1,000.18		$1,050.3868	$1,050.38	$1,050.30	$1,050.40