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	$130.37	5.270%	$137.2405	$137.24	$137.25	$137.20
Purchase #2	$199.45	9.767%	$218.9303	$218.93	$218.95	$218.90
Purchase #3	$240.65	8.191%	$260.3616	$260.36	$260.35	$260.40
Purchase #4	$95.38	5.702%	$100.8186	$100.82	$100.80	$100.80
Purchase #5	$100.27	3.554%	$103.8336	$103.83	$103.85	$103.80
Purchase #6	$153.54	5.649%	$162.2135	$162.21	$162.20	$162.20
Purchase #7	$10.65	3.851%	$11.0601	$11.06	$11.05	$11.10
7 purchase totals =	$930.31		$994.4582	$994.45	$994.45	$994.40