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	$120.74	6.437%	$128.512	$128.51	$128.50	$128.50
Purchase #2	$237.67	13.435%	$269.601	$269.60	$269.60	$269.60
Purchase #3	$43.56	7.510%	$46.8314	$46.83	$46.85	$46.80
Purchase #4	$38.27	6.116%	$40.6106	$40.61	$40.60	$40.60
Purchase #5	$209.31	7.744%	$225.519	$225.52	$225.50	$225.50
Purchase #6	$204.55	7.436%	$219.7603	$219.76	$219.75	$219.80
Purchase #7	$7.29	6.380%	$7.7551	$7.76	$7.75	$7.80
7 purchase totals =	$861.39		$938.5894	$938.59	$938.55	$938.60