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	$18.37	8.313%	$19.8971	$19.90	$19.90	$19.90
Purchase #2	$207.30	7.516%	$222.8807	$222.88	$222.90	$222.90
Purchase #3	$214.71	7.874%	$231.6163	$231.62	$231.60	$231.60
Purchase #4	$37.47	3.343%	$38.7226	$38.72	$38.70	$38.70
Purchase #5	$69.35	4.298%	$72.3307	$72.33	$72.35	$72.30
Purchase #6	$71.65	12.220%	$80.4056	$80.41	$80.40	$80.40
Purchase #7	$81.66	9.855%	$89.7076	$89.71	$89.70	$89.70
7 purchase totals =	$700.51		$755.5606	$755.57	$755.55	$755.50