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	$23.58	3.818%	$24.4803	$24.48	$24.50	$24.50
Purchase #2	$166.61	7.775%	$179.5639	$179.56	$179.55	$179.60
Purchase #3	$86.34	5.278%	$90.897	$90.90	$90.90	$90.90
Purchase #4	$30.85	4.467%	$32.2281	$32.23	$32.25	$32.20
Purchase #5	$103.77	12.586%	$116.8305	$116.83	$116.85	$116.80
Purchase #6	$68.70	4.214%	$71.595	$71.60	$71.60	$71.60
Purchase #7	$77.92	6.681%	$83.1258	$83.13	$83.15	$83.10
7 purchase totals =	$557.77		$598.7206	$598.73	$598.80	$598.70