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	$49.40	5.669%	$52.2005	$52.20	$52.20	$52.20
Purchase #2	$127.50	10.618%	$141.038	$141.04	$141.05	$141.00
Purchase #3	$40.34	13.790%	$45.9029	$45.90	$45.90	$45.90
Purchase #4	$141.53	6.398%	$150.5851	$150.59	$150.60	$150.60
Purchase #5	$55.71	13.655%	$63.3172	$63.32	$63.30	$63.30
Purchase #6	$228.64	7.368%	$245.4862	$245.49	$245.50	$245.50
Purchase #7	$86.79	13.259%	$98.2975	$98.30	$98.30	$98.30
7 purchase totals =	$729.91		$796.8274	$796.84	$796.85	$796.80