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	$26.85	9.405%	$29.3752	$29.38	$29.40	$29.40
Purchase #2	$200.89	13.663%	$228.3376	$228.34	$228.35	$228.30
Purchase #3	$119.54	7.601%	$128.6262	$128.63	$128.65	$128.60
Purchase #4	$150.37	12.568%	$169.2685	$169.27	$169.25	$169.30
Purchase #5	$60.75	6.688%	$64.813	$64.81	$64.80	$64.80
Purchase #6	$86.45	11.750%	$96.6079	$96.61	$96.60	$96.60
Purchase #7	$139.52	3.167%	$143.9386	$143.94	$143.95	$143.90
7 purchase totals =	$784.37		$860.9670	$860.98	$861.00	$860.90