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	$28.47	8.543%	$30.9022	$30.90	$30.90	$30.90
Purchase #2	$102.84	11.195%	$114.3529	$114.35	$114.35	$114.40
Purchase #3	$71.39	12.647%	$80.4187	$80.42	$80.40	$80.40
Purchase #4	$181.61	4.600%	$189.9641	$189.96	$189.95	$190.00
Purchase #5	$22.81	6.302%	$24.2475	$24.25	$24.25	$24.20
Purchase #6	$171.35	8.241%	$185.471	$185.47	$185.45	$185.50
Purchase #7	$41.25	6.151%	$43.7873	$43.79	$43.80	$43.80
7 purchase totals =	$619.72		$669.1437	$669.14	$669.10	$669.20