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	$52.27	10.108%	$57.5535	$57.55	$57.55	$57.60
Purchase #2	$73.38	6.322%	$78.0191	$78.02	$78.00	$78.00
Purchase #3	$178.58	8.731%	$194.1718	$194.17	$194.15	$194.20
Purchase #4	$76.48	10.484%	$84.4982	$84.50	$84.50	$84.50
Purchase #5	$153.55	13.207%	$173.8293	$173.83	$173.85	$173.80
Purchase #6	$103.39	7.370%	$111.0098	$111.01	$111.00	$111.00
Purchase #7	$83.73	9.645%	$91.8058	$91.81	$91.80	$91.80
7 purchase totals =	$721.38		$790.8875	$790.89	$790.85	$790.90