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	$99.73	13.507%	$113.2005	$113.20	$113.20	$113.20
Purchase #2	$91.58	7.409%	$98.3652	$98.37	$98.35	$98.40
Purchase #3	$75.86	8.638%	$82.4128	$82.41	$82.40	$82.40
Purchase #4	$82.25	6.356%	$87.4778	$87.48	$87.50	$87.50
Purchase #5	$239.62	4.672%	$250.815	$250.82	$250.80	$250.80
Purchase #6	$24.60	3.351%	$25.4243	$25.42	$25.40	$25.40
Purchase #7	$137.42	4.302%	$143.3318	$143.33	$143.35	$143.30
7 purchase totals =	$751.06		$801.0274	$801.03	$801.00	$801.00