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	$49.91	9.746%	$54.7742	$54.77	$54.75	$54.80
Purchase #2	$185.38	13.502%	$210.41	$210.41	$210.40	$210.40
Purchase #3	$31.91	3.115%	$32.904	$32.90	$32.90	$32.90
Purchase #4	$150.60	4.224%	$156.9613	$156.96	$156.95	$157.00
Purchase #5	$217.73	13.280%	$246.6445	$246.64	$246.65	$246.60
Purchase #6	$175.41	11.389%	$195.3874	$195.39	$195.40	$195.40
Purchase #7	$101.91	7.695%	$109.752	$109.75	$109.75	$109.80
7 purchase totals =	$912.85		$1,006.8334	$1,006.82	$1,006.80	$1,006.90