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	$186.43	3.513%	$192.9793	$192.98	$193.00	$193.00
Purchase #2	$135.30	4.871%	$141.8905	$141.89	$141.90	$141.90
Purchase #3	$119.99	6.151%	$127.3706	$127.37	$127.35	$127.40
Purchase #4	$55.53	7.774%	$59.8469	$59.85	$59.85	$59.80
Purchase #5	$57.42	3.358%	$59.3482	$59.35	$59.35	$59.30
Purchase #6	$52.62	4.570%	$55.0247	$55.02	$55.00	$55.00
Purchase #7	$94.27	6.118%	$100.0374	$100.04	$100.05	$100.00
7 purchase totals =	$701.56		$736.4976	$736.50	$736.50	$736.40