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	$79.46	6.376%	$84.5264	$84.53	$84.55	$84.50
Purchase #2	$36.25	12.751%	$40.8722	$40.87	$40.85	$40.90
Purchase #3	$122.32	7.769%	$131.823	$131.82	$131.80	$131.80
Purchase #4	$202.58	11.696%	$226.2738	$226.27	$226.25	$226.30
Purchase #5	$209.35	8.854%	$227.8858	$227.89	$227.90	$227.90
Purchase #6	$112.90	10.471%	$124.7218	$124.72	$124.70	$124.70
Purchase #7	$188.61	11.824%	$210.9112	$210.91	$210.90	$210.90
7 purchase totals =	$951.47		$1,047.0142	$1,047.01	$1,046.95	$1,047.00