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	$97.56	6.508%	$103.9092	$103.91	$103.90	$103.90
Purchase #2	$221.37	11.838%	$247.5758	$247.58	$247.60	$247.60
Purchase #3	$96.36	7.424%	$103.5138	$103.51	$103.50	$103.50
Purchase #4	$82.81	9.355%	$90.5569	$90.56	$90.55	$90.60
Purchase #5	$240.81	8.288%	$260.7683	$260.77	$260.75	$260.80
Purchase #6	$40.36	4.382%	$42.1286	$42.13	$42.15	$42.10
Purchase #7	$101.67	10.656%	$112.504	$112.50	$112.50	$112.50
7 purchase totals =	$880.94		$960.9566	$960.96	$960.95	$961.00