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	$54.31	10.332%	$59.9213	$59.92	$59.90	$59.90
Purchase #2	$209.77	11.853%	$234.634	$234.63	$234.65	$234.60
Purchase #3	$106.89	10.188%	$117.78	$117.78	$117.80	$117.80
Purchase #4	$65.67	11.293%	$73.0861	$73.09	$73.10	$73.10
Purchase #5	$40.31	12.529%	$45.3604	$45.36	$45.35	$45.40
Purchase #6	$145.95	4.484%	$152.4944	$152.49	$152.50	$152.50
Purchase #7	$175.67	13.800%	$199.9125	$199.91	$199.90	$199.90
7 purchase totals =	$798.57		$883.1887	$883.18	$883.20	$883.20