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	$46.87	6.712%	$50.0159	$50.02	$50.00	$50.00
Purchase #2	$173.82	7.352%	$186.5992	$186.60	$186.60	$186.60
Purchase #3	$243.53	11.197%	$270.7981	$270.80	$270.80	$270.80
Purchase #4	$133.90	13.128%	$151.4784	$151.48	$151.50	$151.50
Purchase #5	$247.85	3.532%	$256.6041	$256.60	$256.60	$256.60
Purchase #6	$156.56	7.564%	$168.4022	$168.40	$168.40	$168.40
Purchase #7	$5.73	10.117%	$6.3097	$6.31	$6.30	$6.30
7 purchase totals =	$1,008.26		$1,090.2076	$1,090.21	$1,090.20	$1,090.20