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	$117.56	13.606%	$133.5552	$133.56	$133.55	$133.60
Purchase #2	$58.98	3.449%	$61.0142	$61.01	$61.00	$61.00
Purchase #3	$138.75	13.116%	$156.9485	$156.95	$156.95	$156.90
Purchase #4	$7.46	4.826%	$7.82	$7.82	$7.80	$7.80
Purchase #5	$121.51	13.690%	$138.1447	$138.14	$138.15	$138.10
Purchase #6	$43.36	4.344%	$45.2436	$45.24	$45.25	$45.20
Purchase #7	$55.99	3.231%	$57.799	$57.80	$57.80	$57.80
7 purchase totals =	$543.61		$600.5252	$600.52	$600.50	$600.40