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	$134.33	11.685%	$150.0265	$150.03	$150.05	$150.00
Purchase #2	$152.59	5.402%	$160.8329	$160.83	$160.85	$160.80
Purchase #3	$80.36	6.762%	$85.7939	$85.79	$85.80	$85.80
Purchase #4	$169.41	4.493%	$177.0216	$177.02	$177.00	$177.00
Purchase #5	$16.71	6.293%	$17.7616	$17.76	$17.75	$17.80
Purchase #6	$100.34	11.158%	$111.5359	$111.54	$111.55	$111.50
Purchase #7	$140.72	10.790%	$155.9037	$155.90	$155.90	$155.90
7 purchase totals =	$794.46		$858.8761	$858.87	$858.90	$858.80