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	$138.53	9.754%	$152.0422	$152.04	$152.05	$152.00
Purchase #2	$87.31	4.746%	$91.4537	$91.45	$91.45	$91.50
Purchase #3	$124.73	5.285%	$131.322	$131.32	$131.30	$131.30
Purchase #4	$246.73	3.110%	$254.4033	$254.40	$254.40	$254.40
Purchase #5	$144.65	12.326%	$162.4796	$162.48	$162.50	$162.50
Purchase #6	$27.41	12.677%	$30.8848	$30.88	$30.90	$30.90
Purchase #7	$10.57	10.732%	$11.7044	$11.70	$11.70	$11.70
7 purchase totals =	$779.93		$834.2900	$834.27	$834.30	$834.30