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	$169.86	12.446%	$191.0008	$191.00	$191.00	$191.00
Purchase #2	$122.63	9.260%	$133.9855	$133.99	$134.00	$134.00
Purchase #3	$152.48	4.765%	$159.7457	$159.75	$159.75	$159.70
Purchase #4	$24.46	12.449%	$27.505	$27.51	$27.50	$27.50
Purchase #5	$19.73	3.785%	$20.4768	$20.48	$20.50	$20.50
Purchase #6	$154.61	5.363%	$162.9017	$162.90	$162.90	$162.90
Purchase #7	$99.71	11.857%	$111.5326	$111.53	$111.55	$111.50
7 purchase totals =	$743.48		$807.1481	$807.16	$807.20	$807.10