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	$202.42	4.281%	$211.0856	$211.09	$211.10	$211.10
Purchase #2	$64.83	12.421%	$72.8825	$72.88	$72.90	$72.90
Purchase #3	$238.87	13.181%	$270.3555	$270.36	$270.35	$270.40
Purchase #4	$247.91	7.266%	$265.9231	$265.92	$265.90	$265.90
Purchase #5	$18.55	5.820%	$19.6296	$19.63	$19.65	$19.60
Purchase #6	$32.42	8.598%	$35.2075	$35.21	$35.20	$35.20
Purchase #7	$109.85	12.238%	$123.2934	$123.29	$123.30	$123.30
7 purchase totals =	$914.85		$998.3772	$998.38	$998.40	$998.40