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	$24.72	13.668%	$28.0987	$28.10	$28.10	$28.10
Purchase #2	$241.46	8.822%	$262.7616	$262.76	$262.75	$262.80
Purchase #3	$65.31	3.774%	$67.7748	$67.77	$67.75	$67.80
Purchase #4	$218.87	6.493%	$233.0812	$233.08	$233.10	$233.10
Purchase #5	$149.36	12.743%	$168.3929	$168.39	$168.40	$168.40
Purchase #6	$125.26	4.826%	$131.305	$131.31	$131.30	$131.30
Purchase #7	$201.68	12.757%	$227.4083	$227.41	$227.40	$227.40
7 purchase totals =	$1,026.66		$1,118.8225	$1,118.82	$1,118.80	$1,118.90