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	$36.46	9.542%	$39.939	$39.94	$39.95	$39.90
Purchase #2	$140.43	8.413%	$152.2444	$152.24	$152.25	$152.20
Purchase #3	$162.44	7.444%	$174.532	$174.53	$174.55	$174.50
Purchase #4	$169.75	7.131%	$181.8549	$181.85	$181.85	$181.90
Purchase #5	$175.94	5.647%	$185.8753	$185.88	$185.90	$185.90
Purchase #6	$178.56	5.561%	$188.4897	$188.49	$188.50	$188.50
Purchase #7	$228.57	11.606%	$255.0978	$255.10	$255.10	$255.10
7 purchase totals =	$1,092.15		$1,178.0331	$1,178.03	$1,178.10	$1,178.00