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	$217.38	10.824%	$240.9092	$240.91	$240.90	$240.90
Purchase #2	$42.55	4.466%	$44.4503	$44.45	$44.45	$44.50
Purchase #3	$73.33	12.511%	$82.5043	$82.50	$82.50	$82.50
Purchase #4	$166.42	11.684%	$185.8645	$185.86	$185.85	$185.90
Purchase #5	$168.31	7.690%	$181.253	$181.25	$181.25	$181.30
Purchase #6	$27.82	3.238%	$28.7208	$28.72	$28.70	$28.70
Purchase #7	$112.97	4.570%	$118.1327	$118.13	$118.15	$118.10
7 purchase totals =	$808.78		$881.8348	$881.82	$881.80	$881.90