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	$136.32	13.340%	$154.5051	$154.51	$154.50	$154.50
Purchase #2	$135.96	4.566%	$142.1679	$142.17	$142.15	$142.20
Purchase #3	$77.63	5.228%	$81.6885	$81.69	$81.70	$81.70
Purchase #4	$37.27	4.484%	$38.9412	$38.94	$38.95	$38.90
Purchase #5	$130.94	4.743%	$137.1505	$137.15	$137.15	$137.20
Purchase #6	$175.38	11.732%	$195.9556	$195.96	$195.95	$196.00
Purchase #7	$49.75	7.363%	$53.4131	$53.41	$53.40	$53.40
7 purchase totals =	$743.25		$803.8219	$803.83	$803.80	$803.90