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	$56.38	13.306%	$63.8819	$63.88	$63.90	$63.90
Purchase #2	$48.53	10.263%	$53.5106	$53.51	$53.50	$53.50
Purchase #3	$140.29	8.479%	$152.1852	$152.19	$152.20	$152.20
Purchase #4	$138.50	5.616%	$146.2782	$146.28	$146.30	$146.30
Purchase #5	$59.61	13.157%	$67.4529	$67.45	$67.45	$67.50
Purchase #6	$213.57	6.460%	$227.3666	$227.37	$227.35	$227.40
Purchase #7	$200.38	9.237%	$218.8891	$218.89	$218.90	$218.90
7 purchase totals =	$857.26		$929.5645	$929.57	$929.60	$929.70