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	$223.93	11.846%	$250.4567	$250.46	$250.45	$250.50
Purchase #2	$105.30	5.843%	$111.4527	$111.45	$111.45	$111.50
Purchase #3	$62.39	4.728%	$65.3398	$65.34	$65.35	$65.30
Purchase #4	$67.39	9.717%	$73.9383	$73.94	$73.95	$73.90
Purchase #5	$77.35	8.469%	$83.9008	$83.90	$83.90	$83.90
Purchase #6	$55.73	8.547%	$60.4932	$60.49	$60.50	$60.50
Purchase #7	$162.26	11.783%	$181.3791	$181.38	$181.40	$181.40
7 purchase totals =	$754.35		$826.9606	$826.96	$827.00	$827.00