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	$43.98	13.460%	$49.8997	$49.90	$49.90	$49.90
Purchase #2	$198.53	12.580%	$223.5051	$223.51	$223.50	$223.50
Purchase #3	$210.94	5.274%	$222.065	$222.07	$222.05	$222.10
Purchase #4	$36.36	10.242%	$40.084	$40.08	$40.10	$40.10
Purchase #5	$35.35	6.471%	$37.6375	$37.64	$37.65	$37.60
Purchase #6	$81.27	12.653%	$91.5531	$91.55	$91.55	$91.60
Purchase #7	$240.93	6.810%	$257.3373	$257.34	$257.35	$257.30
7 purchase totals =	$847.36		$922.0817	$922.09	$922.10	$922.10