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	$138.96	12.622%	$156.4995	$156.50	$156.50	$156.50
Purchase #2	$24.79	7.102%	$26.5506	$26.55	$26.55	$26.60
Purchase #3	$196.47	10.639%	$217.3724	$217.37	$217.35	$217.40
Purchase #4	$25.96	12.201%	$29.1274	$29.13	$29.15	$29.10
Purchase #5	$96.28	3.369%	$99.5237	$99.52	$99.50	$99.50
Purchase #6	$229.89	11.565%	$256.4768	$256.48	$256.50	$256.50
Purchase #7	$218.26	6.447%	$232.3312	$232.33	$232.35	$232.30
7 purchase totals =	$930.61		$1,017.8816	$1,017.88	$1,017.90	$1,017.90