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	$122.95	3.874%	$127.7131	$127.71	$127.70	$127.70
Purchase #2	$133.75	3.823%	$138.8633	$138.86	$138.85	$138.90
Purchase #3	$214.33	9.136%	$233.9112	$233.91	$233.90	$233.90
Purchase #4	$161.56	4.511%	$168.848	$168.85	$168.85	$168.80
Purchase #5	$81.98	3.104%	$84.5247	$84.52	$84.50	$84.50
Purchase #6	$123.79	3.278%	$127.8478	$127.85	$127.85	$127.80
Purchase #7	$237.94	13.267%	$269.5075	$269.51	$269.50	$269.50
7 purchase totals =	$1,076.30		$1,151.2156	$1,151.21	$1,151.15	$1,151.10