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	$12.59	7.859%	$13.5794	$13.58	$13.60	$13.60
Purchase #2	$185.40	11.232%	$206.2241	$206.22	$206.20	$206.20
Purchase #3	$164.69	9.623%	$180.5381	$180.54	$180.55	$180.50
Purchase #4	$55.57	6.443%	$59.1504	$59.15	$59.15	$59.20
Purchase #5	$194.49	7.359%	$208.8025	$208.80	$208.80	$208.80
Purchase #6	$240.32	7.379%	$258.0532	$258.05	$258.05	$258.10
Purchase #7	$243.54	8.597%	$264.4771	$264.48	$264.50	$264.50
7 purchase totals =	$1,096.60		$1,190.8248	$1,190.82	$1,190.85	$1,190.90