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	$120.85	13.476%	$137.1357	$137.14	$137.15	$137.10
Purchase #2	$166.74	11.142%	$185.3182	$185.32	$185.30	$185.30
Purchase #3	$104.85	13.582%	$119.0907	$119.09	$119.10	$119.10
Purchase #4	$42.34	7.676%	$45.59	$45.59	$45.60	$45.60
Purchase #5	$15.95	6.743%	$17.0255	$17.03	$17.05	$17.00
Purchase #6	$79.84	3.590%	$82.7063	$82.71	$82.70	$82.70
Purchase #7	$208.33	5.419%	$219.6194	$219.62	$219.60	$219.60
7 purchase totals =	$738.90		$806.4858	$806.50	$806.50	$806.40