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	$235.74	11.782%	$263.5149	$263.51	$263.50	$263.50
Purchase #2	$208.57	5.328%	$219.6826	$219.68	$219.70	$219.70
Purchase #3	$173.66	4.123%	$180.82	$180.82	$180.80	$180.80
Purchase #4	$166.40	11.470%	$185.4861	$185.49	$185.50	$185.50
Purchase #5	$45.66	12.250%	$51.2534	$51.25	$51.25	$51.30
Purchase #6	$168.54	13.529%	$191.3418	$191.34	$191.35	$191.30
Purchase #7	$33.31	7.230%	$35.7183	$35.72	$35.70	$35.70
7 purchase totals =	$1,031.88		$1,127.8171	$1,127.81	$1,127.80	$1,127.80