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	$165.47	11.870%	$185.1113	$185.11	$185.10	$185.10
Purchase #2	$104.77	3.540%	$108.4789	$108.48	$108.50	$108.50
Purchase #3	$31.40	13.665%	$35.6908	$35.69	$35.70	$35.70
Purchase #4	$27.92	7.139%	$29.9132	$29.91	$29.90	$29.90
Purchase #5	$219.78	8.615%	$238.714	$238.71	$238.70	$238.70
Purchase #6	$39.68	6.376%	$42.21	$42.21	$42.20	$42.20
Purchase #7	$250.76	3.687%	$260.0055	$260.01	$260.00	$260.00
7 purchase totals =	$839.78		$900.1237	$900.12	$900.10	$900.10