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	$36.44	6.805%	$38.9197	$38.92	$38.90	$38.90
Purchase #2	$48.27	12.719%	$54.4095	$54.41	$54.40	$54.40
Purchase #3	$180.49	4.841%	$189.2275	$189.23	$189.25	$189.20
Purchase #4	$125.30	13.527%	$142.2493	$142.25	$142.25	$142.20
Purchase #5	$161.74	10.390%	$178.5448	$178.54	$178.55	$178.50
Purchase #6	$130.47	5.789%	$138.0229	$138.02	$138.00	$138.00
Purchase #7	$40.81	5.253%	$42.9537	$42.95	$42.95	$43.00
7 purchase totals =	$723.52		$784.3274	$784.32	$784.30	$784.20