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	$186.38	12.740%	$210.1248	$210.12	$210.10	$210.10
Purchase #2	$80.45	3.500%	$83.2658	$83.27	$83.25	$83.30
Purchase #3	$103.95	5.557%	$109.7265	$109.73	$109.75	$109.70
Purchase #4	$74.53	12.685%	$83.9841	$83.98	$84.00	$84.00
Purchase #5	$221.28	4.658%	$231.5872	$231.59	$231.60	$231.60
Purchase #6	$139.67	8.746%	$151.8855	$151.89	$151.90	$151.90
Purchase #7	$63.78	10.635%	$70.563	$70.56	$70.55	$70.60
7 purchase totals =	$870.04		$941.1369	$941.14	$941.15	$941.20