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	$174.66	5.276%	$183.8751	$183.88	$183.90	$183.90
Purchase #2	$133.53	12.518%	$150.2453	$150.25	$150.25	$150.20
Purchase #3	$36.96	4.678%	$38.689	$38.69	$38.70	$38.70
Purchase #4	$95.69	3.237%	$98.7875	$98.79	$98.80	$98.80
Purchase #5	$185.69	7.447%	$199.5183	$199.52	$199.50	$199.50
Purchase #6	$140.31	11.841%	$156.9241	$156.92	$156.90	$156.90
Purchase #7	$225.29	11.376%	$250.919	$250.92	$250.90	$250.90
7 purchase totals =	$992.13		$1,078.9583	$1,078.97	$1,078.95	$1,078.90