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	$154.95	9.222%	$169.2395	$169.24	$169.25	$169.20
Purchase #2	$198.69	3.457%	$205.5587	$205.56	$205.55	$205.60
Purchase #3	$19.80	9.282%	$21.6378	$21.64	$21.65	$21.60
Purchase #4	$152.72	10.537%	$168.8121	$168.81	$168.80	$168.80
Purchase #5	$19.40	12.491%	$21.8233	$21.82	$21.80	$21.80
Purchase #6	$193.76	7.362%	$208.0246	$208.02	$208.00	$208.00
Purchase #7	$39.46	8.535%	$42.8279	$42.83	$42.85	$42.80
7 purchase totals =	$778.78		$837.9239	$837.92	$837.90	$837.80