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	$151.61	12.850%	$171.0919	$171.09	$171.10	$171.10
Purchase #2	$221.83	8.288%	$240.2153	$240.22	$240.20	$240.20
Purchase #3	$172.95	5.270%	$182.0645	$182.06	$182.05	$182.10
Purchase #4	$137.38	8.221%	$148.674	$148.67	$148.65	$148.70
Purchase #5	$78.31	12.669%	$88.2311	$88.23	$88.25	$88.20
Purchase #6	$57.47	4.159%	$59.8602	$59.86	$59.85	$59.90
Purchase #7	$131.34	5.414%	$138.4507	$138.45	$138.45	$138.50
7 purchase totals =	$950.89		$1,028.5877	$1,028.58	$1,028.55	$1,028.70