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	$171.47	5.485%	$180.8751	$180.88	$180.90	$180.90
Purchase #2	$124.99	9.518%	$136.8865	$136.89	$136.90	$136.90
Purchase #3	$78.51	11.576%	$87.5983	$87.60	$87.60	$87.60
Purchase #4	$152.84	11.508%	$170.4288	$170.43	$170.45	$170.40
Purchase #5	$147.39	3.492%	$152.5369	$152.54	$152.55	$152.50
Purchase #6	$238.82	12.222%	$268.0086	$268.01	$268.00	$268.00
Purchase #7	$86.58	5.298%	$91.167	$91.17	$91.15	$91.20
7 purchase totals =	$1,000.60		$1,087.5012	$1,087.52	$1,087.55	$1,087.50