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	$14.90	3.792%	$15.465	$15.47	$15.45	$15.50
Purchase #2	$232.63	7.848%	$250.8868	$250.89	$250.90	$250.90
Purchase #3	$12.68	9.566%	$13.893	$13.89	$13.90	$13.90
Purchase #4	$31.47	3.207%	$32.4792	$32.48	$32.50	$32.50
Purchase #5	$212.46	10.800%	$235.4057	$235.41	$235.40	$235.40
Purchase #6	$209.53	4.361%	$218.6676	$218.67	$218.65	$218.70
Purchase #7	$31.90	4.443%	$33.3173	$33.32	$33.30	$33.30
7 purchase totals =	$745.57		$800.1146	$800.13	$800.10	$800.20