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	$25.82	13.190%	$29.2257	$29.23	$29.25	$29.20
Purchase #2	$158.53	8.800%	$172.4806	$172.48	$172.50	$172.50
Purchase #3	$119.26	3.799%	$123.7907	$123.79	$123.80	$123.80
Purchase #4	$147.35	3.775%	$152.9125	$152.91	$152.90	$152.90
Purchase #5	$192.95	3.787%	$200.257	$200.26	$200.25	$200.30
Purchase #6	$243.92	12.532%	$274.4881	$274.49	$274.50	$274.50
Purchase #7	$111.73	7.774%	$120.4159	$120.42	$120.40	$120.40
7 purchase totals =	$999.56		$1,073.5705	$1,073.58	$1,073.60	$1,073.60