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	$84.39	7.270%	$90.5252	$90.53	$90.55	$90.50
Purchase #2	$87.41	12.370%	$98.2226	$98.22	$98.20	$98.20
Purchase #3	$206.81	5.608%	$218.4079	$218.41	$218.40	$218.40
Purchase #4	$222.44	9.183%	$242.8667	$242.87	$242.85	$242.90
Purchase #5	$66.38	9.319%	$72.566	$72.57	$72.55	$72.60
Purchase #6	$111.39	6.228%	$118.3274	$118.33	$118.35	$118.30
Purchase #7	$105.57	9.423%	$115.5179	$115.52	$115.50	$115.50
7 purchase totals =	$884.39		$956.4337	$956.45	$956.40	$956.40