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	$42.40	12.871%	$47.8573	$47.86	$47.85	$47.90
Purchase #2	$95.90	7.726%	$103.3092	$103.31	$103.30	$103.30
Purchase #3	$82.89	3.112%	$85.4695	$85.47	$85.45	$85.50
Purchase #4	$228.37	6.819%	$243.9426	$243.94	$243.95	$243.90
Purchase #5	$29.30	11.308%	$32.6132	$32.61	$32.60	$32.60
Purchase #6	$16.84	4.140%	$17.5372	$17.54	$17.55	$17.50
Purchase #7	$68.44	9.776%	$75.1307	$75.13	$75.15	$75.10
7 purchase totals =	$564.14		$605.8597	$605.86	$605.85	$605.80