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	$224.95	11.400%	$250.5943	$250.59	$250.60	$250.60
Purchase #2	$208.41	9.708%	$228.6424	$228.64	$228.65	$228.60
Purchase #3	$130.54	13.335%	$147.9475	$147.95	$147.95	$147.90
Purchase #4	$202.60	4.179%	$211.0667	$211.07	$211.05	$211.10
Purchase #5	$37.58	10.834%	$41.6514	$41.65	$41.65	$41.70
Purchase #6	$42.88	13.544%	$48.6877	$48.69	$48.70	$48.70
Purchase #7	$85.53	5.554%	$90.2803	$90.28	$90.30	$90.30
7 purchase totals =	$932.49		$1,018.8703	$1,018.87	$1,018.90	$1,018.90