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	$124.40	12.667%	$140.1577	$140.16	$140.15	$140.20
Purchase #2	$151.59	10.566%	$167.607	$167.61	$167.60	$167.60
Purchase #3	$108.33	8.809%	$117.8728	$117.87	$117.85	$117.90
Purchase #4	$42.48	11.220%	$47.2463	$47.25	$47.25	$47.20
Purchase #5	$100.38	4.389%	$104.7857	$104.79	$104.80	$104.80
Purchase #6	$72.90	9.818%	$80.0573	$80.06	$80.05	$80.10
Purchase #7	$85.84	9.330%	$93.8489	$93.85	$93.85	$93.80
7 purchase totals =	$685.92		$751.5757	$751.59	$751.55	$751.60