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	$92.76	6.739%	$99.0111	$99.01	$99.00	$99.00
Purchase #2	$188.96	6.231%	$200.7341	$200.73	$200.75	$200.70
Purchase #3	$173.96	6.645%	$185.5196	$185.52	$185.50	$185.50
Purchase #4	$7.47	6.120%	$7.9272	$7.93	$7.95	$7.90
Purchase #5	$180.70	6.435%	$192.328	$192.33	$192.35	$192.30
Purchase #6	$193.45	6.245%	$205.531	$205.53	$205.55	$205.50
Purchase #7	$26.34	4.830%	$27.6122	$27.61	$27.60	$27.60
7 purchase totals =	$863.64		$918.6632	$918.66	$918.70	$918.50