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	$71.43	13.853%	$81.3252	$81.33	$81.35	$81.30
Purchase #2	$43.30	4.744%	$45.3542	$45.35	$45.35	$45.40
Purchase #3	$194.76	8.754%	$211.8093	$211.81	$211.80	$211.80
Purchase #4	$194.75	7.788%	$209.9171	$209.92	$209.90	$209.90
Purchase #5	$78.26	4.779%	$82	$82.00	$82.00	$82.00
Purchase #6	$224.38	3.228%	$231.623	$231.62	$231.60	$231.60
Purchase #7	$228.89	3.473%	$236.8393	$236.84	$236.85	$236.80
7 purchase totals =	$1,035.77		$1,098.8681	$1,098.87	$1,098.85	$1,098.80