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	$71.67	12.152%	$80.3793	$80.38	$80.40	$80.40
Purchase #2	$27.72	4.175%	$28.8773	$28.88	$28.90	$28.90
Purchase #3	$168.61	8.786%	$183.4241	$183.42	$183.40	$183.40
Purchase #4	$243.27	7.872%	$262.4202	$262.42	$262.40	$262.40
Purchase #5	$161.66	6.803%	$172.6577	$172.66	$172.65	$172.70
Purchase #6	$41.38	4.825%	$43.3766	$43.38	$43.40	$43.40
Purchase #7	$136.55	3.688%	$141.586	$141.59	$141.60	$141.60
7 purchase totals =	$850.86		$912.7212	$912.73	$912.75	$912.80