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	$100.59	10.270%	$110.9206	$110.92	$110.90	$110.90
Purchase #2	$176.58	10.689%	$195.4546	$195.45	$195.45	$195.50
Purchase #3	$131.52	9.154%	$143.5593	$143.56	$143.55	$143.60
Purchase #4	$59.44	12.531%	$66.8884	$66.89	$66.90	$66.90
Purchase #5	$196.99	8.433%	$213.6022	$213.60	$213.60	$213.60
Purchase #6	$30.49	9.421%	$33.3625	$33.36	$33.35	$33.40
Purchase #7	$221.81	7.488%	$238.4191	$238.42	$238.40	$238.40
7 purchase totals =	$917.42		$1,002.2067	$1,002.20	$1,002.15	$1,002.30