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	$112.48	3.430%	$116.3381	$116.34	$116.35	$116.30
Purchase #2	$108.45	13.674%	$123.2795	$123.28	$123.30	$123.30
Purchase #3	$136.30	11.167%	$151.5206	$151.52	$151.50	$151.50
Purchase #4	$163.78	3.812%	$170.0233	$170.02	$170.00	$170.00
Purchase #5	$75.88	13.112%	$85.8294	$85.83	$85.85	$85.80
Purchase #6	$129.36	9.500%	$141.6492	$141.65	$141.65	$141.60
Purchase #7	$98.27	4.107%	$102.3059	$102.31	$102.30	$102.30
7 purchase totals =	$824.52		$890.9460	$890.95	$890.95	$890.80