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	$36.66	5.428%	$38.6499	$38.65	$38.65	$38.60
Purchase #2	$188.63	12.710%	$212.6049	$212.60	$212.60	$212.60
Purchase #3	$53.88	10.120%	$59.3327	$59.33	$59.35	$59.30
Purchase #4	$98.59	5.432%	$103.9454	$103.95	$103.95	$103.90
Purchase #5	$224.66	9.265%	$245.4747	$245.47	$245.45	$245.50
Purchase #6	$48.32	7.518%	$51.9527	$51.95	$51.95	$52.00
Purchase #7	$35.35	12.869%	$39.8992	$39.90	$39.90	$39.90
7 purchase totals =	$686.09		$751.8595	$751.85	$751.85	$751.80