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	$172.63	3.774%	$179.1451	$179.15	$179.15	$179.10
Purchase #2	$106.60	12.491%	$119.9154	$119.92	$119.90	$119.90
Purchase #3	$62.87	13.602%	$71.4216	$71.42	$71.40	$71.40
Purchase #4	$139.96	12.257%	$157.1149	$157.11	$157.10	$157.10
Purchase #5	$150.50	13.306%	$170.5255	$170.53	$170.55	$170.50
Purchase #6	$123.63	6.670%	$131.8761	$131.88	$131.90	$131.90
Purchase #7	$178.56	5.228%	$187.8951	$187.90	$187.90	$187.90
7 purchase totals =	$934.75		$1,017.8937	$1,017.91	$1,017.90	$1,017.80