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	$53.94	3.577%	$55.8694	$55.87	$55.85	$55.90
Purchase #2	$45.65	8.409%	$49.4887	$49.49	$49.50	$49.50
Purchase #3	$225.96	6.414%	$240.4531	$240.45	$240.45	$240.50
Purchase #4	$181.35	8.295%	$196.393	$196.39	$196.40	$196.40
Purchase #5	$106.55	12.814%	$120.2033	$120.20	$120.20	$120.20
Purchase #6	$247.80	7.136%	$265.483	$265.48	$265.50	$265.50
Purchase #7	$86.38	6.849%	$92.2962	$92.30	$92.30	$92.30
7 purchase totals =	$947.63		$1,020.1867	$1,020.18	$1,020.20	$1,020.30