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	$168.29	6.602%	$179.4005	$179.40	$179.40	$179.40
Purchase #2	$195.87	13.815%	$222.9294	$222.93	$222.95	$222.90
Purchase #3	$204.31	13.454%	$231.7979	$231.80	$231.80	$231.80
Purchase #4	$67.46	7.448%	$72.4844	$72.48	$72.50	$72.50
Purchase #5	$135.30	3.777%	$140.4103	$140.41	$140.40	$140.40
Purchase #6	$137.50	8.807%	$149.6096	$149.61	$149.60	$149.60
Purchase #7	$19.53	9.254%	$21.3373	$21.34	$21.35	$21.30
7 purchase totals =	$928.26		$1,017.9694	$1,017.97	$1,018.00	$1,017.90