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	$150.32	5.193%	$158.1261	$158.13	$158.15	$158.10
Purchase #2	$34.31	9.377%	$37.5272	$37.53	$37.55	$37.50
Purchase #3	$189.97	3.312%	$196.2618	$196.26	$196.25	$196.30
Purchase #4	$161.87	3.803%	$168.0259	$168.03	$168.05	$168.00
Purchase #5	$66.99	4.414%	$69.9469	$69.95	$69.95	$69.90
Purchase #6	$77.59	9.751%	$85.1558	$85.16	$85.15	$85.20
Purchase #7	$39.28	7.598%	$42.2645	$42.26	$42.25	$42.30
7 purchase totals =	$720.33		$757.3082	$757.32	$757.35	$757.30