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	$245.42	9.873%	$269.6503	$269.65	$269.65	$269.70
Purchase #2	$124.33	9.600%	$136.2657	$136.27	$136.25	$136.30
Purchase #3	$29.89	5.766%	$31.6135	$31.61	$31.60	$31.60
Purchase #4	$44.91	11.112%	$49.9004	$49.90	$49.90	$49.90
Purchase #5	$57.64	9.502%	$63.117	$63.12	$63.10	$63.10
Purchase #6	$144.54	9.545%	$158.3363	$158.34	$158.35	$158.30
Purchase #7	$101.71	3.377%	$105.1447	$105.14	$105.15	$105.10
7 purchase totals =	$748.44		$814.0279	$814.03	$814.00	$814.00