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	$78.32	12.582%	$88.1742	$88.17	$88.15	$88.20
Purchase #2	$63.77	12.579%	$71.7916	$71.79	$71.80	$71.80
Purchase #3	$47.35	13.112%	$53.5585	$53.56	$53.55	$53.60
Purchase #4	$40.54	9.805%	$44.5149	$44.51	$44.50	$44.50
Purchase #5	$77.73	3.349%	$80.3332	$80.33	$80.35	$80.30
Purchase #6	$45.82	10.850%	$50.7915	$50.79	$50.80	$50.80
Purchase #7	$179.51	11.398%	$199.9705	$199.97	$199.95	$200.00
7 purchase totals =	$533.04		$589.1344	$589.12	$589.10	$589.20