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	$236.35	9.313%	$258.3613	$258.36	$258.35	$258.40
Purchase #2	$55.41	6.498%	$59.0105	$59.01	$59.00	$59.00
Purchase #3	$233.45	6.797%	$249.3176	$249.32	$249.30	$249.30
Purchase #4	$35.99	5.418%	$37.9399	$37.94	$37.95	$37.90
Purchase #5	$190.95	9.282%	$208.674	$208.67	$208.65	$208.70
Purchase #6	$121.75	10.601%	$134.6567	$134.66	$134.65	$134.70
Purchase #7	$130.88	13.428%	$148.4546	$148.45	$148.45	$148.50
7 purchase totals =	$1,004.78		$1,096.4146	$1,096.41	$1,096.35	$1,096.50