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	$82.54	9.612%	$90.4737	$90.47	$90.45	$90.50
Purchase #2	$136.94	3.619%	$141.8959	$141.90	$141.90	$141.90
Purchase #3	$27.85	7.424%	$29.9176	$29.92	$29.90	$29.90
Purchase #4	$155.80	6.835%	$166.4489	$166.45	$166.45	$166.40
Purchase #5	$240.61	9.872%	$264.363	$264.36	$264.35	$264.40
Purchase #6	$21.60	5.196%	$22.7223	$22.72	$22.70	$22.70
Purchase #7	$46.36	12.227%	$52.0284	$52.03	$52.05	$52.00
7 purchase totals =	$711.70		$767.8498	$767.85	$767.80	$767.80