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	$34.96	12.686%	$39.395	$39.40	$39.40	$39.40
Purchase #2	$87.79	13.634%	$99.7593	$99.76	$99.75	$99.80
Purchase #3	$97.39	12.596%	$109.6572	$109.66	$109.65	$109.70
Purchase #4	$250.63	9.155%	$273.5752	$273.58	$273.60	$273.60
Purchase #5	$177.33	12.495%	$199.4874	$199.49	$199.50	$199.50
Purchase #6	$72.30	4.441%	$75.5108	$75.51	$75.50	$75.50
Purchase #7	$40.85	3.374%	$42.2283	$42.23	$42.25	$42.20
7 purchase totals =	$761.25		$839.6132	$839.63	$839.65	$839.70