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	$90.61	11.825%	$101.3246	$101.32	$101.30	$101.30
Purchase #2	$36.37	6.671%	$38.7962	$38.80	$38.80	$38.80
Purchase #3	$62.97	5.269%	$66.2879	$66.29	$66.30	$66.30
Purchase #4	$96.91	3.245%	$100.0547	$100.05	$100.05	$100.10
Purchase #5	$167.52	10.135%	$184.4982	$184.50	$184.50	$184.50
Purchase #6	$37.93	12.151%	$42.5389	$42.54	$42.55	$42.50
Purchase #7	$82.39	6.870%	$88.0502	$88.05	$88.05	$88.10
7 purchase totals =	$574.70		$621.5507	$621.55	$621.55	$621.60