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	$71.53	9.226%	$78.1294	$78.13	$78.15	$78.10
Purchase #2	$199.44	11.379%	$222.1343	$222.13	$222.15	$222.10
Purchase #3	$113.56	9.544%	$124.3982	$124.40	$124.40	$124.40
Purchase #4	$49.88	6.631%	$53.1875	$53.19	$53.20	$53.20
Purchase #5	$186.82	11.297%	$207.9251	$207.93	$207.95	$207.90
Purchase #6	$56.94	9.355%	$62.2667	$62.27	$62.25	$62.30
Purchase #7	$29.65	9.141%	$32.3603	$32.36	$32.35	$32.40
7 purchase totals =	$707.82		$780.4015	$780.41	$780.45	$780.40