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	$142.66	4.229%	$148.6931	$148.69	$148.70	$148.70
Purchase #2	$208.86	7.151%	$223.7956	$223.80	$223.80	$223.80
Purchase #3	$62.70	12.253%	$70.3826	$70.38	$70.40	$70.40
Purchase #4	$125.45	4.798%	$131.4691	$131.47	$131.45	$131.50
Purchase #5	$18.90	5.140%	$19.8715	$19.87	$19.85	$19.90
Purchase #6	$180.34	5.164%	$189.6528	$189.65	$189.65	$189.70
Purchase #7	$29.87	5.262%	$31.4418	$31.44	$31.45	$31.40
7 purchase totals =	$768.78		$815.3065	$815.30	$815.30	$815.40