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	$128.90	6.409%	$137.1612	$137.16	$137.15	$137.20
Purchase #2	$180.57	13.717%	$205.3388	$205.34	$205.35	$205.30
Purchase #3	$27.32	9.294%	$29.8591	$29.86	$29.85	$29.90
Purchase #4	$86.36	10.302%	$95.2568	$95.26	$95.25	$95.30
Purchase #5	$167.63	10.639%	$185.4642	$185.46	$185.45	$185.50
Purchase #6	$73.81	11.789%	$82.5115	$82.51	$82.50	$82.50
Purchase #7	$76.96	12.799%	$86.8101	$86.81	$86.80	$86.80
7 purchase totals =	$741.55		$822.4017	$822.40	$822.35	$822.50