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	$215.82	11.317%	$240.2443	$240.24	$240.25	$240.20
Purchase #2	$58.33	4.848%	$61.1578	$61.16	$61.15	$61.20
Purchase #3	$121.70	4.586%	$127.2812	$127.28	$127.30	$127.30
Purchase #4	$19.65	8.151%	$21.2517	$21.25	$21.25	$21.30
Purchase #5	$112.38	9.642%	$123.2157	$123.22	$123.20	$123.20
Purchase #6	$116.65	9.112%	$127.2791	$127.28	$127.30	$127.30
Purchase #7	$123.98	8.591%	$134.6311	$134.63	$134.65	$134.60
7 purchase totals =	$768.51		$835.0609	$835.06	$835.10	$835.10