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	$7.70	7.644%	$8.2886	$8.29	$8.30	$8.30
Purchase #2	$249.66	13.731%	$283.9408	$283.94	$283.95	$283.90
Purchase #3	$124.92	13.245%	$141.4657	$141.47	$141.45	$141.50
Purchase #4	$75.58	8.835%	$82.2575	$82.26	$82.25	$82.30
Purchase #5	$98.34	7.223%	$105.4431	$105.44	$105.45	$105.40
Purchase #6	$241.31	10.790%	$267.3473	$267.35	$267.35	$267.30
Purchase #7	$121.80	7.430%	$130.8497	$130.85	$130.85	$130.80
7 purchase totals =	$919.31		$1,019.5927	$1,019.60	$1,019.60	$1,019.50