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	$47.88	12.601%	$53.9134	$53.91	$53.90	$53.90
Purchase #2	$216.35	8.494%	$234.7268	$234.73	$234.75	$234.70
Purchase #3	$174.80	12.518%	$196.6815	$196.68	$196.70	$196.70
Purchase #4	$102.42	6.538%	$109.1162	$109.12	$109.10	$109.10
Purchase #5	$203.33	7.659%	$218.903	$218.90	$218.90	$218.90
Purchase #6	$130.57	5.466%	$137.707	$137.71	$137.70	$137.70
Purchase #7	$168.40	4.707%	$176.3266	$176.33	$176.35	$176.30
7 purchase totals =	$1,043.75		$1,127.3745	$1,127.38	$1,127.40	$1,127.30