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	$71.90	13.791%	$81.8157	$81.82	$81.80	$81.80
Purchase #2	$208.79	4.611%	$218.4173	$218.42	$218.40	$218.40
Purchase #3	$183.37	12.626%	$206.5223	$206.52	$206.50	$206.50
Purchase #4	$148.73	7.834%	$160.3815	$160.38	$160.40	$160.40
Purchase #5	$179.59	11.547%	$200.3273	$200.33	$200.35	$200.30
Purchase #6	$167.61	10.310%	$184.8906	$184.89	$184.90	$184.90
Purchase #7	$244.27	12.269%	$274.2395	$274.24	$274.25	$274.20
7 purchase totals =	$1,204.26		$1,326.5942	$1,326.60	$1,326.60	$1,326.50