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	$10.56	12.496%	$11.8796	$11.88	$11.90	$11.90
Purchase #2	$51.26	12.303%	$57.5665	$57.57	$57.55	$57.60
Purchase #3	$247.54	13.862%	$281.854	$281.85	$281.85	$281.90
Purchase #4	$87.40	10.369%	$96.4625	$96.46	$96.45	$96.50
Purchase #5	$34.82	7.417%	$37.4026	$37.40	$37.40	$37.40
Purchase #6	$134.93	11.301%	$150.1784	$150.18	$150.20	$150.20
Purchase #7	$183.37	9.527%	$200.8397	$200.84	$200.85	$200.80
7 purchase totals =	$749.88		$836.1833	$836.18	$836.20	$836.30