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	$90.30	9.647%	$99.0112	$99.01	$99.00	$99.00
Purchase #2	$36.40	10.787%	$40.3265	$40.33	$40.35	$40.30
Purchase #3	$199.89	13.595%	$227.065	$227.07	$227.05	$227.10
Purchase #4	$53.78	10.696%	$59.5323	$59.53	$59.55	$59.50
Purchase #5	$82.68	8.649%	$89.831	$89.83	$89.85	$89.80
Purchase #6	$134.30	10.871%	$148.8998	$148.90	$148.90	$148.90
Purchase #7	$184.25	10.259%	$203.1522	$203.15	$203.15	$203.20
7 purchase totals =	$781.60		$867.8180	$867.82	$867.85	$867.80