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	$155.90	5.769%	$164.8939	$164.89	$164.90	$164.90
Purchase #2	$37.29	9.714%	$40.9124	$40.91	$40.90	$40.90
Purchase #3	$27.53	3.285%	$28.4344	$28.43	$28.45	$28.40
Purchase #4	$71.86	10.690%	$79.5418	$79.54	$79.55	$79.50
Purchase #5	$88.49	6.436%	$94.1852	$94.19	$94.20	$94.20
Purchase #6	$219.46	4.611%	$229.5793	$229.58	$229.60	$229.60
Purchase #7	$135.61	8.689%	$147.3932	$147.39	$147.40	$147.40
7 purchase totals =	$736.14		$784.9402	$784.93	$785.00	$784.90