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	$94.59	6.584%	$100.8178	$100.82	$100.80	$100.80
Purchase #2	$62.41	7.354%	$66.9996	$67.00	$67.00	$67.00
Purchase #3	$90.48	6.728%	$96.5675	$96.57	$96.55	$96.60
Purchase #4	$220.34	7.484%	$236.8302	$236.83	$236.85	$236.80
Purchase #5	$81.88	5.325%	$86.2401	$86.24	$86.25	$86.20
Purchase #6	$70.64	10.752%	$78.2352	$78.24	$78.25	$78.20
Purchase #7	$159.46	13.358%	$180.7607	$180.76	$180.75	$180.80
7 purchase totals =	$779.80		$846.4511	$846.46	$846.45	$846.40