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	$247.50	6.843%	$264.4364	$264.44	$264.45	$264.40
Purchase #2	$136.57	4.201%	$142.3073	$142.31	$142.30	$142.30
Purchase #3	$146.58	6.578%	$156.222	$156.22	$156.20	$156.20
Purchase #4	$84.64	3.409%	$87.5254	$87.53	$87.55	$87.50
Purchase #5	$206.70	4.204%	$215.3897	$215.39	$215.40	$215.40
Purchase #6	$78.73	9.249%	$86.0117	$86.01	$86.00	$86.00
Purchase #7	$88.64	12.370%	$99.6048	$99.60	$99.60	$99.60
7 purchase totals =	$989.36		$1,051.4973	$1,051.50	$1,051.50	$1,051.40