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	$78.32	3.330%	$80.9281	$80.93	$80.95	$80.90
Purchase #2	$122.92	10.690%	$136.0601	$136.06	$136.05	$136.10
Purchase #3	$71.51	3.299%	$73.8691	$73.87	$73.85	$73.90
Purchase #4	$143.38	10.459%	$158.3761	$158.38	$158.40	$158.40
Purchase #5	$28.64	9.815%	$31.451	$31.45	$31.45	$31.50
Purchase #6	$63.79	6.800%	$68.1277	$68.13	$68.15	$68.10
Purchase #7	$82.72	4.370%	$86.3349	$86.33	$86.35	$86.30
7 purchase totals =	$591.28		$635.1470	$635.15	$635.20	$635.20