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	$174.92	6.228%	$185.814	$185.81	$185.80	$185.80
Purchase #2	$132.59	13.789%	$150.8728	$150.87	$150.85	$150.90
Purchase #3	$178.88	9.523%	$195.9147	$195.91	$195.90	$195.90
Purchase #4	$62.97	11.258%	$70.0592	$70.06	$70.05	$70.10
Purchase #5	$202.71	9.589%	$222.1479	$222.15	$222.15	$222.10
Purchase #6	$151.56	6.838%	$161.9237	$161.92	$161.90	$161.90
Purchase #7	$102.55	3.575%	$106.2162	$106.22	$106.20	$106.20
7 purchase totals =	$1,006.18		$1,092.9485	$1,092.94	$1,092.85	$1,092.90