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	$243.40	4.408%	$254.1291	$254.13	$254.15	$254.10
Purchase #2	$245.70	13.795%	$279.5943	$279.59	$279.60	$279.60
Purchase #3	$232.89	11.241%	$259.0692	$259.07	$259.05	$259.10
Purchase #4	$37.57	12.353%	$42.211	$42.21	$42.20	$42.20
Purchase #5	$172.73	7.229%	$185.2167	$185.22	$185.20	$185.20
Purchase #6	$52.61	5.183%	$55.3368	$55.34	$55.35	$55.30
Purchase #7	$218.35	13.600%	$248.0456	$248.05	$248.05	$248.00
7 purchase totals =	$1,203.25		$1,323.6027	$1,323.61	$1,323.60	$1,323.50