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	$208.98	10.847%	$231.6481	$231.65	$231.65	$231.60
Purchase #2	$153.59	10.456%	$169.6494	$169.65	$169.65	$169.60
Purchase #3	$40.68	12.279%	$45.6751	$45.68	$45.70	$45.70
Purchase #4	$52.45	4.776%	$54.955	$54.96	$54.95	$55.00
Purchase #5	$205.33	4.190%	$213.9333	$213.93	$213.95	$213.90
Purchase #6	$139.73	9.843%	$153.4836	$153.48	$153.50	$153.50
Purchase #7	$103.57	7.659%	$111.5024	$111.50	$111.50	$111.50
7 purchase totals =	$904.33		$980.8469	$980.85	$980.90	$980.80