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	$36.94	10.514%	$40.8239	$40.82	$40.80	$40.80
Purchase #2	$160.53	10.148%	$176.8206	$176.82	$176.80	$176.80
Purchase #3	$163.38	11.772%	$182.6131	$182.61	$182.60	$182.60
Purchase #4	$85.85	4.382%	$89.6119	$89.61	$89.60	$89.60
Purchase #5	$225.64	9.187%	$246.3695	$246.37	$246.35	$246.40
Purchase #6	$19.61	6.399%	$20.8648	$20.86	$20.85	$20.90
Purchase #7	$60.43	11.416%	$67.3287	$67.33	$67.35	$67.30
7 purchase totals =	$752.38		$824.4325	$824.42	$824.35	$824.40