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	$139.26	6.552%	$148.3843	$148.38	$148.40	$148.40
Purchase #2	$50.80	9.179%	$55.4629	$55.46	$55.45	$55.50
Purchase #3	$24.42	4.314%	$25.4735	$25.47	$25.45	$25.50
Purchase #4	$250.89	8.322%	$271.7691	$271.77	$271.75	$271.80
Purchase #5	$208.98	9.253%	$228.3169	$228.32	$228.30	$228.30
Purchase #6	$55.42	9.463%	$60.6644	$60.66	$60.65	$60.70
Purchase #7	$150.25	12.165%	$168.5279	$168.53	$168.55	$168.50
7 purchase totals =	$880.02		$958.5990	$958.59	$958.55	$958.70