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	$12.34	6.260%	$13.1125	$13.11	$13.10	$13.10
Purchase #2	$192.62	6.678%	$205.4832	$205.48	$205.50	$205.50
Purchase #3	$171.48	9.124%	$187.1258	$187.13	$187.15	$187.10
Purchase #4	$57.92	10.299%	$63.8852	$63.89	$63.90	$63.90
Purchase #5	$183.28	5.506%	$193.3714	$193.37	$193.35	$193.40
Purchase #6	$71.53	10.366%	$78.9448	$78.94	$78.95	$78.90
Purchase #7	$140.55	12.811%	$158.5559	$158.56	$158.55	$158.60
7 purchase totals =	$829.72		$900.4788	$900.48	$900.50	$900.50