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	$37.45	7.202%	$40.1471	$40.15	$40.15	$40.10
Purchase #2	$168.87	9.695%	$185.2419	$185.24	$185.25	$185.20
Purchase #3	$167.80	13.404%	$190.2919	$190.29	$190.30	$190.30
Purchase #4	$139.86	11.343%	$155.7243	$155.72	$155.70	$155.70
Purchase #5	$196.84	8.169%	$212.9199	$212.92	$212.90	$212.90
Purchase #6	$113.67	6.212%	$120.7312	$120.73	$120.75	$120.70
Purchase #7	$74.53	10.661%	$82.4756	$82.48	$82.50	$82.50
7 purchase totals =	$899.02		$987.5319	$987.53	$987.55	$987.40