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	$56.33	10.281%	$62.1213	$62.12	$62.10	$62.10
Purchase #2	$226.85	12.702%	$255.6645	$255.66	$255.65	$255.70
Purchase #3	$47.66	5.166%	$50.1221	$50.12	$50.10	$50.10
Purchase #4	$82.54	3.429%	$85.3703	$85.37	$85.35	$85.40
Purchase #5	$80.80	10.789%	$89.5175	$89.52	$89.50	$89.50
Purchase #6	$77.35	5.868%	$81.8889	$81.89	$81.90	$81.90
Purchase #7	$27.78	12.386%	$31.2208	$31.22	$31.20	$31.20
7 purchase totals =	$599.31		$655.9054	$655.90	$655.80	$655.90