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	$234.80	12.560%	$264.2909	$264.29	$264.30	$264.30
Purchase #2	$200.66	12.490%	$225.7224	$225.72	$225.70	$225.70
Purchase #3	$75.64	4.237%	$78.8449	$78.84	$78.85	$78.80
Purchase #4	$50.94	10.667%	$56.3738	$56.37	$56.35	$56.40
Purchase #5	$53.96	10.816%	$59.7963	$59.80	$59.80	$59.80
Purchase #6	$200.32	10.818%	$221.9906	$221.99	$222.00	$222.00
Purchase #7	$109.59	9.193%	$119.6646	$119.66	$119.65	$119.70
7 purchase totals =	$925.91		$1,026.6835	$1,026.67	$1,026.65	$1,026.70