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	$166.73	13.546%	$189.3152	$189.32	$189.30	$189.30
Purchase #2	$119.38	3.262%	$123.2742	$123.27	$123.25	$123.30
Purchase #3	$151.35	9.408%	$165.589	$165.59	$165.60	$165.60
Purchase #4	$200.51	8.497%	$217.5473	$217.55	$217.55	$217.50
Purchase #5	$194.46	8.375%	$210.746	$210.75	$210.75	$210.70
Purchase #6	$42.59	3.170%	$43.9401	$43.94	$43.95	$43.90
Purchase #7	$125.33	4.490%	$130.9573	$130.96	$130.95	$131.00
7 purchase totals =	$1,000.35		$1,081.3691	$1,081.38	$1,081.35	$1,081.30