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	$151.58	5.567%	$160.0185	$160.02	$160.00	$160.00
Purchase #2	$248.49	11.331%	$276.6464	$276.65	$276.65	$276.60
Purchase #3	$56.81	13.493%	$64.4754	$64.48	$64.50	$64.50
Purchase #4	$51.41	8.678%	$55.8714	$55.87	$55.85	$55.90
Purchase #5	$130.89	6.616%	$139.5497	$139.55	$139.55	$139.50
Purchase #6	$76.36	9.123%	$83.3263	$83.33	$83.35	$83.30
Purchase #7	$200.33	11.794%	$223.9569	$223.96	$223.95	$224.00
7 purchase totals =	$915.87		$1,003.8446	$1,003.86	$1,003.85	$1,003.80