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	$52.61	8.611%	$57.1402	$57.14	$57.15	$57.10
Purchase #2	$6.62	3.558%	$6.8555	$6.86	$6.85	$6.90
Purchase #3	$74.46	12.566%	$83.8166	$83.82	$83.80	$83.80
Purchase #4	$90.90	11.488%	$101.3426	$101.34	$101.35	$101.30
Purchase #5	$109.56	6.829%	$117.0419	$117.04	$117.05	$117.00
Purchase #6	$31.79	4.633%	$33.2628	$33.26	$33.25	$33.30
Purchase #7	$77.34	3.541%	$80.0786	$80.08	$80.10	$80.10
7 purchase totals =	$443.28		$479.5382	$479.54	$479.55	$479.50