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	$193.37	11.261%	$215.1454	$215.15	$215.15	$215.10
Purchase #2	$202.49	6.341%	$215.3299	$215.33	$215.35	$215.30
Purchase #3	$242.58	9.781%	$266.3067	$266.31	$266.30	$266.30
Purchase #4	$164.37	10.779%	$182.0874	$182.09	$182.10	$182.10
Purchase #5	$33.39	12.318%	$37.503	$37.50	$37.50	$37.50
Purchase #6	$229.46	13.458%	$260.3407	$260.34	$260.35	$260.30
Purchase #7	$134.35	7.288%	$144.1414	$144.14	$144.15	$144.10
7 purchase totals =	$1,200.01		$1,320.8545	$1,320.86	$1,320.90	$1,320.70