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	$50.27	9.275%	$54.9325	$54.93	$54.95	$54.90
Purchase #2	$124.77	5.686%	$131.8644	$131.86	$131.85	$131.90
Purchase #3	$97.47	6.552%	$103.8562	$103.86	$103.85	$103.90
Purchase #4	$41.39	6.552%	$44.1019	$44.10	$44.10	$44.10
Purchase #5	$60.73	10.467%	$67.0866	$67.09	$67.10	$67.10
Purchase #6	$99.33	7.259%	$106.5404	$106.54	$106.55	$106.50
Purchase #7	$34.61	4.451%	$36.1505	$36.15	$36.15	$36.20
7 purchase totals =	$508.57		$544.5325	$544.53	$544.55	$544.60