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	$122.65	7.272%	$131.5691	$131.57	$131.55	$131.60
Purchase #2	$47.66	5.401%	$50.2341	$50.23	$50.25	$50.20
Purchase #3	$109.36	9.624%	$119.8848	$119.88	$119.90	$119.90
Purchase #4	$185.77	3.134%	$191.592	$191.59	$191.60	$191.60
Purchase #5	$19.78	5.593%	$20.8863	$20.89	$20.90	$20.90
Purchase #6	$7.31	12.624%	$8.2328	$8.23	$8.25	$8.20
Purchase #7	$22.87	7.264%	$24.5313	$24.53	$24.55	$24.50
7 purchase totals =	$515.40		$546.9304	$546.92	$547.00	$546.90