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	$37.78	13.771%	$42.9827	$42.98	$43.00	$43.00
Purchase #2	$219.33	7.564%	$235.9201	$235.92	$235.90	$235.90
Purchase #3	$124.93	8.838%	$135.9713	$135.97	$135.95	$136.00
Purchase #4	$77.86	13.631%	$88.4731	$88.47	$88.45	$88.50
Purchase #5	$82.97	7.535%	$89.2218	$89.22	$89.20	$89.20
Purchase #6	$153.62	12.573%	$172.9346	$172.93	$172.95	$172.90
Purchase #7	$195.89	11.705%	$218.8189	$218.82	$218.80	$218.80
7 purchase totals =	$892.38		$984.3225	$984.31	$984.25	$984.30