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	$133.73	13.858%	$152.2623	$152.26	$152.25	$152.30
Purchase #2	$221.81	3.150%	$228.797	$228.80	$228.80	$228.80
Purchase #3	$230.84	12.334%	$259.3118	$259.31	$259.30	$259.30
Purchase #4	$164.81	10.637%	$182.3408	$182.34	$182.35	$182.30
Purchase #5	$179.86	4.819%	$188.5275	$188.53	$188.55	$188.50
Purchase #6	$82.71	9.357%	$90.4492	$90.45	$90.45	$90.40
Purchase #7	$216.36	10.161%	$238.3443	$238.34	$238.35	$238.30
7 purchase totals =	$1,230.12		$1,340.0329	$1,340.03	$1,340.05	$1,339.90