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	$35.57	11.711%	$39.7356	$39.74	$39.75	$39.70
Purchase #2	$220.43	10.480%	$243.5311	$243.53	$243.55	$243.50
Purchase #3	$142.72	5.661%	$150.7994	$150.80	$150.80	$150.80
Purchase #4	$203.48	9.592%	$222.9978	$223.00	$223.00	$223.00
Purchase #5	$112.82	13.363%	$127.8961	$127.90	$127.90	$127.90
Purchase #6	$76.56	10.265%	$84.4189	$84.42	$84.40	$84.40
Purchase #7	$131.94	10.330%	$145.5694	$145.57	$145.55	$145.60
7 purchase totals =	$923.52		$1,014.9483	$1,014.96	$1,014.95	$1,014.90