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	$33.35	13.315%	$37.7906	$37.79	$37.80	$37.80
Purchase #2	$166.79	5.248%	$175.5431	$175.54	$175.55	$175.50
Purchase #3	$38.56	13.823%	$43.8901	$43.89	$43.90	$43.90
Purchase #4	$103.33	12.640%	$116.3909	$116.39	$116.40	$116.40
Purchase #5	$198.44	11.520%	$221.3003	$221.30	$221.30	$221.30
Purchase #6	$181.98	3.506%	$188.3602	$188.36	$188.35	$188.40
Purchase #7	$145.34	5.705%	$153.6316	$153.63	$153.65	$153.60
7 purchase totals =	$867.79		$936.9068	$936.90	$936.95	$936.90