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	$142.29	12.237%	$159.702	$159.70	$159.70	$159.70
Purchase #2	$72.72	11.331%	$80.9599	$80.96	$80.95	$81.00
Purchase #3	$229.83	8.579%	$249.5471	$249.55	$249.55	$249.50
Purchase #4	$174.99	12.298%	$196.5103	$196.51	$196.50	$196.50
Purchase #5	$215.86	7.580%	$232.2222	$232.22	$232.20	$232.20
Purchase #6	$207.86	3.248%	$214.6113	$214.61	$214.60	$214.60
Purchase #7	$88.34	13.109%	$99.9205	$99.92	$99.90	$99.90
7 purchase totals =	$1,131.89		$1,233.4733	$1,233.47	$1,233.40	$1,233.40