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	$177.57	6.669%	$189.4121	$189.41	$189.40	$189.40
Purchase #2	$174.31	6.367%	$185.4083	$185.41	$185.40	$185.40
Purchase #3	$28.73	11.192%	$31.9455	$31.95	$31.95	$31.90
Purchase #4	$175.25	4.817%	$183.6918	$183.69	$183.70	$183.70
Purchase #5	$228.27	5.799%	$241.5074	$241.51	$241.50	$241.50
Purchase #6	$244.47	4.640%	$255.8134	$255.81	$255.80	$255.80
Purchase #7	$186.72	3.165%	$192.6297	$192.63	$192.65	$192.60
7 purchase totals =	$1,215.32		$1,280.4082	$1,280.41	$1,280.40	$1,280.30