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	$136.31	3.568%	$141.1735	$141.17	$141.15	$141.20
Purchase #2	$18.57	12.789%	$20.9449	$20.94	$20.95	$20.90
Purchase #3	$158.32	9.647%	$173.5931	$173.59	$173.60	$173.60
Purchase #4	$169.73	12.104%	$190.2741	$190.27	$190.25	$190.30
Purchase #5	$44.99	12.279%	$50.5143	$50.51	$50.50	$50.50
Purchase #6	$233.86	8.270%	$253.2002	$253.20	$253.20	$253.20
Purchase #7	$130.96	9.870%	$143.8858	$143.89	$143.90	$143.90
7 purchase totals =	$892.74		$973.5859	$973.57	$973.55	$973.60