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	$5.40	11.536%	$6.0229	$6.02	$6.00	$6.00
Purchase #2	$87.57	7.696%	$94.3094	$94.31	$94.30	$94.30
Purchase #3	$134.52	5.764%	$142.2737	$142.27	$142.25	$142.30
Purchase #4	$202.89	11.333%	$225.8835	$225.88	$225.90	$225.90
Purchase #5	$108.34	10.561%	$119.7818	$119.78	$119.80	$119.80
Purchase #6	$90.47	9.777%	$99.3153	$99.32	$99.30	$99.30
Purchase #7	$45.65	9.158%	$49.8306	$49.83	$49.85	$49.80
7 purchase totals =	$674.84		$737.4172	$737.41	$737.40	$737.40