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	$106.76	4.729%	$111.8087	$111.81	$111.80	$111.80
Purchase #2	$149.90	9.644%	$164.3564	$164.36	$164.35	$164.40
Purchase #3	$61.82	9.737%	$67.8394	$67.84	$67.85	$67.80
Purchase #4	$128.57	5.812%	$136.0425	$136.04	$136.05	$136.00
Purchase #5	$32.55	10.261%	$35.89	$35.89	$35.90	$35.90
Purchase #6	$11.70	10.447%	$12.9223	$12.92	$12.90	$12.90
Purchase #7	$135.76	5.859%	$143.7142	$143.71	$143.70	$143.70
7 purchase totals =	$627.06		$672.5735	$672.57	$672.55	$672.50