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	$245.33	7.579%	$263.9236	$263.92	$263.90	$263.90
Purchase #2	$112.94	10.691%	$125.0144	$125.01	$125.00	$125.00
Purchase #3	$30.25	10.296%	$33.3645	$33.36	$33.35	$33.40
Purchase #4	$189.26	3.815%	$196.4803	$196.48	$196.50	$196.50
Purchase #5	$36.56	6.699%	$39.0092	$39.01	$39.00	$39.00
Purchase #6	$149.97	11.235%	$166.8191	$166.82	$166.80	$166.80
Purchase #7	$83.94	8.248%	$90.8634	$90.86	$90.85	$90.90
7 purchase totals =	$848.25		$915.4745	$915.46	$915.40	$915.50