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	$28.31	11.302%	$31.5096	$31.51	$31.50	$31.50
Purchase #2	$29.35	7.774%	$31.6317	$31.63	$31.65	$31.60
Purchase #3	$136.91	5.613%	$144.5948	$144.59	$144.60	$144.60
Purchase #4	$121.28	8.437%	$131.5124	$131.51	$131.50	$131.50
Purchase #5	$167.89	10.170%	$184.9644	$184.96	$184.95	$185.00
Purchase #6	$37.40	6.356%	$39.7771	$39.78	$39.80	$39.80
Purchase #7	$189.91	7.152%	$203.4924	$203.49	$203.50	$203.50
7 purchase totals =	$711.05		$767.4824	$767.47	$767.50	$767.50