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	$113.57	13.483%	$128.8826	$128.88	$128.90	$128.90
Purchase #2	$99.38	13.455%	$112.7516	$112.75	$112.75	$112.80
Purchase #3	$131.28	9.370%	$143.5809	$143.58	$143.60	$143.60
Purchase #4	$119.54	9.807%	$131.2633	$131.26	$131.25	$131.30
Purchase #5	$36.90	12.166%	$41.3893	$41.39	$41.40	$41.40
Purchase #6	$65.67	9.815%	$72.1155	$72.12	$72.10	$72.10
Purchase #7	$75.99	7.279%	$81.5213	$81.52	$81.50	$81.50
7 purchase totals =	$642.33		$711.5045	$711.50	$711.50	$711.60