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	$78.78	4.778%	$82.5441	$82.54	$82.55	$82.50
Purchase #2	$225.77	7.578%	$242.8789	$242.88	$242.90	$242.90
Purchase #3	$6.90	13.494%	$7.8311	$7.83	$7.85	$7.80
Purchase #4	$137.77	9.483%	$150.8347	$150.83	$150.85	$150.80
Purchase #5	$157.68	5.600%	$166.5101	$166.51	$166.50	$166.50
Purchase #6	$28.75	3.840%	$29.854	$29.85	$29.85	$29.90
Purchase #7	$80.82	3.790%	$83.8831	$83.88	$83.90	$83.90
7 purchase totals =	$716.47		$764.3360	$764.32	$764.40	$764.30