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	$242.38	8.576%	$263.1665	$263.17	$263.15	$263.20
Purchase #2	$88.44	9.235%	$96.6074	$96.61	$96.60	$96.60
Purchase #3	$196.89	13.435%	$223.3422	$223.34	$223.35	$223.30
Purchase #4	$98.34	4.199%	$102.4693	$102.47	$102.45	$102.50
Purchase #5	$68.91	9.159%	$75.2215	$75.22	$75.20	$75.20
Purchase #6	$40.58	6.786%	$43.3338	$43.33	$43.35	$43.30
Purchase #7	$53.99	9.596%	$59.1709	$59.17	$59.15	$59.20
7 purchase totals =	$789.53		$863.3116	$863.31	$863.25	$863.30