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	$175.48	9.704%	$192.5086	$192.51	$192.50	$192.50
Purchase #2	$162.96	3.638%	$168.8885	$168.89	$168.90	$168.90
Purchase #3	$130.51	12.103%	$146.3056	$146.31	$146.30	$146.30
Purchase #4	$123.74	13.123%	$139.9784	$139.98	$140.00	$140.00
Purchase #5	$71.36	6.338%	$75.8828	$75.88	$75.90	$75.90
Purchase #6	$84.95	11.141%	$94.4143	$94.41	$94.40	$94.40
Purchase #7	$6.92	7.631%	$7.4481	$7.45	$7.45	$7.40
7 purchase totals =	$755.92		$825.4263	$825.43	$825.45	$825.40