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	$77.61	5.609%	$81.9631	$81.96	$81.95	$82.00
Purchase #2	$131.87	8.861%	$143.555	$143.56	$143.55	$143.60
Purchase #3	$73.51	6.744%	$78.4675	$78.47	$78.45	$78.50
Purchase #4	$131.63	6.409%	$140.0662	$140.07	$140.05	$140.10
Purchase #5	$147.90	12.666%	$166.633	$166.63	$166.65	$166.60
Purchase #6	$229.44	12.134%	$257.2802	$257.28	$257.30	$257.30
Purchase #7	$142.96	6.670%	$152.4954	$152.50	$152.50	$152.50
7 purchase totals =	$934.92		$1,020.4604	$1,020.47	$1,020.45	$1,020.60