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	$235.26	12.299%	$264.1946	$264.19	$264.20	$264.20
Purchase #2	$134.56	12.412%	$151.2616	$151.26	$151.25	$151.30
Purchase #3	$123.51	11.253%	$137.4086	$137.41	$137.40	$137.40
Purchase #4	$178.93	9.846%	$196.5474	$196.55	$196.55	$196.50
Purchase #5	$112.35	6.804%	$119.9943	$119.99	$120.00	$120.00
Purchase #6	$206.88	13.549%	$234.9102	$234.91	$234.90	$234.90
Purchase #7	$55.41	11.648%	$61.8642	$61.86	$61.85	$61.90
7 purchase totals =	$1,046.90		$1,166.1809	$1,166.17	$1,166.15	$1,166.20