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	$137.60	3.488%	$142.3995	$142.40	$142.40	$142.40
Purchase #2	$105.56	7.798%	$113.7916	$113.79	$113.80	$113.80
Purchase #3	$157.54	5.431%	$166.096	$166.10	$166.10	$166.10
Purchase #4	$25.79	10.709%	$28.5519	$28.55	$28.55	$28.60
Purchase #5	$97.81	6.213%	$103.8869	$103.89	$103.90	$103.90
Purchase #6	$135.75	10.748%	$150.3404	$150.34	$150.35	$150.30
Purchase #7	$203.32	11.810%	$227.3321	$227.33	$227.35	$227.30
7 purchase totals =	$863.37		$932.3984	$932.40	$932.45	$932.40