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	$29.50	13.417%	$33.458	$33.46	$33.45	$33.50
Purchase #2	$195.45	12.300%	$219.4904	$219.49	$219.50	$219.50
Purchase #3	$190.89	4.241%	$198.9856	$198.99	$199.00	$199.00
Purchase #4	$39.75	9.827%	$43.6562	$43.66	$43.65	$43.70
Purchase #5	$222.43	3.387%	$229.9637	$229.96	$229.95	$230.00
Purchase #6	$125.40	9.802%	$137.6917	$137.69	$137.70	$137.70
Purchase #7	$154.90	8.188%	$167.5832	$167.58	$167.60	$167.60
7 purchase totals =	$958.32		$1,030.8288	$1,030.83	$1,030.85	$1,031.00