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	$102.64	6.386%	$109.1946	$109.19	$109.20	$109.20
Purchase #2	$203.48	9.196%	$222.192	$222.19	$222.20	$222.20
Purchase #3	$47.54	10.159%	$52.3696	$52.37	$52.35	$52.40
Purchase #4	$48.83	8.281%	$52.8736	$52.87	$52.85	$52.90
Purchase #5	$26.43	6.853%	$28.2412	$28.24	$28.25	$28.20
Purchase #6	$167.94	10.827%	$186.1229	$186.12	$186.10	$186.10
Purchase #7	$134.40	8.546%	$145.8858	$145.89	$145.90	$145.90
7 purchase totals =	$731.26		$796.8797	$796.87	$796.85	$796.90