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	$123.52	13.542%	$140.2471	$140.25	$140.25	$140.20
Purchase #2	$207.29	4.626%	$216.8792	$216.88	$216.90	$216.90
Purchase #3	$209.90	4.250%	$218.8208	$218.82	$218.80	$218.80
Purchase #4	$206.54	3.835%	$214.4608	$214.46	$214.45	$214.50
Purchase #5	$99.44	5.382%	$104.7919	$104.79	$104.80	$104.80
Purchase #6	$182.83	12.155%	$205.053	$205.05	$205.05	$205.10
Purchase #7	$168.33	6.535%	$179.3304	$179.33	$179.35	$179.30
7 purchase totals =	$1,197.85		$1,279.5832	$1,279.58	$1,279.60	$1,279.60