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	$124.85	13.639%	$141.8783	$141.88	$141.90	$141.90
Purchase #2	$181.76	8.873%	$197.8876	$197.89	$197.90	$197.90
Purchase #3	$32.29	13.110%	$36.5232	$36.52	$36.50	$36.50
Purchase #4	$240.61	11.411%	$268.066	$268.07	$268.05	$268.10
Purchase #5	$217.90	7.764%	$234.8178	$234.82	$234.80	$234.80
Purchase #6	$65.77	8.396%	$71.292	$71.29	$71.30	$71.30
Purchase #7	$37.47	7.146%	$40.1476	$40.15	$40.15	$40.10
7 purchase totals =	$900.65		$990.6125	$990.62	$990.60	$990.60