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	$240.48	13.730%	$273.4979	$273.50	$273.50	$273.50
Purchase #2	$59.79	11.413%	$66.6138	$66.61	$66.60	$66.60
Purchase #3	$23.37	8.264%	$25.3013	$25.30	$25.30	$25.30
Purchase #4	$138.46	4.736%	$145.0175	$145.02	$145.00	$145.00
Purchase #5	$131.88	6.444%	$140.3783	$140.38	$140.40	$140.40
Purchase #6	$152.51	11.398%	$169.8931	$169.89	$169.90	$169.90
Purchase #7	$196.86	3.554%	$203.8564	$203.86	$203.85	$203.90
7 purchase totals =	$943.35		$1,024.5583	$1,024.56	$1,024.55	$1,024.60