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	$200.52	3.174%	$206.8845	$206.88	$206.90	$206.90
Purchase #2	$122.46	11.492%	$136.5331	$136.53	$136.55	$136.50
Purchase #3	$78.44	8.826%	$85.3631	$85.36	$85.35	$85.40
Purchase #4	$37.87	13.146%	$42.8484	$42.85	$42.85	$42.80
Purchase #5	$75.61	7.570%	$81.3337	$81.33	$81.35	$81.30
Purchase #6	$186.64	12.409%	$209.8002	$209.80	$209.80	$209.80
Purchase #7	$35.43	6.510%	$37.7365	$37.74	$37.75	$37.70
7 purchase totals =	$736.97		$800.4995	$800.49	$800.55	$800.40