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	$51.55	13.505%	$58.5118	$58.51	$58.50	$58.50
Purchase #2	$102.32	12.123%	$114.7243	$114.72	$114.70	$114.70
Purchase #3	$89.48	10.800%	$99.1438	$99.14	$99.15	$99.10
Purchase #4	$76.51	12.861%	$86.35	$86.35	$86.35	$86.40
Purchase #5	$238.33	13.472%	$270.4378	$270.44	$270.45	$270.40
Purchase #6	$149.89	4.341%	$156.3967	$156.40	$156.40	$156.40
Purchase #7	$210.88	4.749%	$220.8947	$220.89	$220.90	$220.90
7 purchase totals =	$918.96		$1,006.4591	$1,006.45	$1,006.45	$1,006.40