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	$29.75	13.298%	$33.7062	$33.71	$33.70	$33.70
Purchase #2	$181.33	13.789%	$206.3336	$206.33	$206.35	$206.30
Purchase #3	$139.75	10.804%	$154.8486	$154.85	$154.85	$154.80
Purchase #4	$142.54	13.172%	$161.3154	$161.32	$161.30	$161.30
Purchase #5	$197.47	13.209%	$223.5538	$223.55	$223.55	$223.60
Purchase #6	$152.41	11.520%	$169.9676	$169.97	$169.95	$170.00
Purchase #7	$97.29	12.380%	$109.3345	$109.33	$109.35	$109.30
7 purchase totals =	$940.54		$1,059.0597	$1,059.06	$1,059.05	$1,059.00