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	$159.45	8.141%	$172.4308	$172.43	$172.45	$172.40
Purchase #2	$135.95	11.865%	$152.0805	$152.08	$152.10	$152.10
Purchase #3	$196.49	3.481%	$203.3298	$203.33	$203.35	$203.30
Purchase #4	$24.51	5.337%	$25.8181	$25.82	$25.80	$25.80
Purchase #5	$55.82	12.506%	$62.8008	$62.80	$62.80	$62.80
Purchase #6	$120.66	12.756%	$136.0514	$136.05	$136.05	$136.10
Purchase #7	$33.35	11.760%	$37.272	$37.27	$37.25	$37.30
7 purchase totals =	$726.23		$789.7834	$789.78	$789.80	$789.80