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	$121.57	13.767%	$138.3065	$138.31	$138.30	$138.30
Purchase #2	$159.92	4.740%	$167.5002	$167.50	$167.50	$167.50
Purchase #3	$110.62	11.196%	$123.005	$123.01	$123.00	$123.00
Purchase #4	$77.50	6.417%	$82.4732	$82.47	$82.45	$82.50
Purchase #5	$89.50	11.280%	$99.5956	$99.60	$99.60	$99.60
Purchase #6	$87.33	13.383%	$99.0174	$99.02	$99.00	$99.00
Purchase #7	$212.93	6.220%	$226.1742	$226.17	$226.15	$226.20
7 purchase totals =	$859.37		$936.0721	$936.08	$936.00	$936.10