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	$40.61	3.865%	$42.1796	$42.18	$42.20	$42.20
Purchase #2	$196.99	13.265%	$223.1207	$223.12	$223.10	$223.10
Purchase #3	$133.58	5.665%	$141.1473	$141.15	$141.15	$141.10
Purchase #4	$164.26	9.170%	$179.3226	$179.32	$179.30	$179.30
Purchase #5	$121.79	10.527%	$134.6108	$134.61	$134.60	$134.60
Purchase #6	$143.54	5.184%	$150.9811	$150.98	$151.00	$151.00
Purchase #7	$196.71	8.229%	$212.8973	$212.90	$212.90	$212.90
7 purchase totals =	$997.48		$1,084.2594	$1,084.26	$1,084.25	$1,084.20