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	$239.70	6.843%	$256.1027	$256.10	$256.10	$256.10
Purchase #2	$213.56	4.381%	$222.9161	$222.92	$222.90	$222.90
Purchase #3	$75.41	4.355%	$78.6941	$78.69	$78.70	$78.70
Purchase #4	$97.99	4.674%	$102.5701	$102.57	$102.55	$102.60
Purchase #5	$90.42	8.497%	$98.103	$98.10	$98.10	$98.10
Purchase #6	$180.93	4.669%	$189.3776	$189.38	$189.40	$189.40
Purchase #7	$45.93	10.815%	$50.8973	$50.90	$50.90	$50.90
7 purchase totals =	$943.94		$998.6609	$998.66	$998.65	$998.70