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	$137.85	13.812%	$156.8898	$156.89	$156.90	$156.90
Purchase #2	$12.60	6.155%	$13.3755	$13.38	$13.40	$13.40
Purchase #3	$182.94	8.393%	$198.2942	$198.29	$198.30	$198.30
Purchase #4	$37.34	13.544%	$42.3973	$42.40	$42.40	$42.40
Purchase #5	$240.43	4.165%	$250.4439	$250.44	$250.45	$250.40
Purchase #6	$44.71	13.773%	$50.8679	$50.87	$50.85	$50.90
Purchase #7	$93.95	3.361%	$97.1077	$97.11	$97.10	$97.10
7 purchase totals =	$749.82		$809.3763	$809.38	$809.40	$809.40