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	$96.89	8.191%	$104.8263	$104.83	$104.85	$104.80
Purchase #2	$55.29	7.447%	$59.4074	$59.41	$59.40	$59.40
Purchase #3	$170.57	8.468%	$185.0139	$185.01	$185.00	$185.00
Purchase #4	$169.76	9.456%	$185.8125	$185.81	$185.80	$185.80
Purchase #5	$142.55	8.776%	$155.0602	$155.06	$155.05	$155.10
Purchase #6	$235.46	9.759%	$258.4385	$258.44	$258.45	$258.40
Purchase #7	$156.48	3.522%	$161.9912	$161.99	$162.00	$162.00
7 purchase totals =	$1,027.00		$1,110.5500	$1,110.55	$1,110.55	$1,110.50