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	$171.86	10.209%	$189.4052	$189.41	$189.40	$189.40
Purchase #2	$121.33	8.600%	$131.7644	$131.76	$131.75	$131.80
Purchase #3	$217.26	4.725%	$227.5255	$227.53	$227.55	$227.50
Purchase #4	$195.90	13.423%	$222.1957	$222.20	$222.20	$222.20
Purchase #5	$33.30	13.419%	$37.7685	$37.77	$37.75	$37.80
Purchase #6	$50.50	6.638%	$53.8522	$53.85	$53.85	$53.90
Purchase #7	$140.75	10.610%	$155.6836	$155.68	$155.70	$155.70
7 purchase totals =	$930.90		$1,018.1951	$1,018.20	$1,018.20	$1,018.30