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	$240.88	9.764%	$264.3995	$264.40	$264.40	$264.40
Purchase #2	$93.61	11.406%	$104.2872	$104.29	$104.30	$104.30
Purchase #3	$91.37	10.592%	$101.0479	$101.05	$101.05	$101.00
Purchase #4	$67.45	5.564%	$71.2029	$71.20	$71.20	$71.20
Purchase #5	$203.67	8.737%	$221.4646	$221.46	$221.45	$221.50
Purchase #6	$22.43	12.684%	$25.275	$25.28	$25.30	$25.30
Purchase #7	$127.89	3.131%	$131.8942	$131.89	$131.90	$131.90
7 purchase totals =	$847.30		$919.5713	$919.57	$919.60	$919.60