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	$248.25	6.362%	$264.0437	$264.04	$264.05	$264.00
Purchase #2	$174.46	12.284%	$195.8907	$195.89	$195.90	$195.90
Purchase #3	$216.36	13.250%	$245.0277	$245.03	$245.05	$245.00
Purchase #4	$25.76	6.789%	$27.5088	$27.51	$27.50	$27.50
Purchase #5	$34.31	9.373%	$37.5259	$37.53	$37.55	$37.50
Purchase #6	$120.68	9.740%	$132.4342	$132.43	$132.45	$132.40
Purchase #7	$83.65	8.268%	$90.5662	$90.57	$90.55	$90.60
7 purchase totals =	$903.47		$992.9972	$993.00	$993.05	$992.90