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	$98.32	4.355%	$102.6018	$102.60	$102.60	$102.60
Purchase #2	$206.34	10.759%	$228.5401	$228.54	$228.55	$228.50
Purchase #3	$83.70	4.869%	$87.7754	$87.78	$87.80	$87.80
Purchase #4	$94.49	7.866%	$101.9226	$101.92	$101.90	$101.90
Purchase #5	$79.52	9.300%	$86.9154	$86.92	$86.90	$86.90
Purchase #6	$63.31	7.235%	$67.8905	$67.89	$67.90	$67.90
Purchase #7	$7.25	6.637%	$7.7312	$7.73	$7.75	$7.70
7 purchase totals =	$632.93		$683.3770	$683.38	$683.40	$683.30