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	$28.54	9.372%	$31.2148	$31.21	$31.20	$31.20
Purchase #2	$150.73	13.827%	$171.5714	$171.57	$171.55	$171.60
Purchase #3	$102.47	6.859%	$109.4984	$109.50	$109.50	$109.50
Purchase #4	$13.65	10.303%	$15.0564	$15.06	$15.05	$15.10
Purchase #5	$211.73	12.153%	$237.4615	$237.46	$237.45	$237.50
Purchase #6	$48.82	10.124%	$53.7625	$53.76	$53.75	$53.80
Purchase #7	$243.56	9.860%	$267.575	$267.58	$267.60	$267.60
7 purchase totals =	$799.50		$886.1400	$886.14	$886.10	$886.30