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	$59.67	3.300%	$61.6391	$61.64	$61.65	$61.60
Purchase #2	$190.61	11.754%	$213.0143	$213.01	$213.00	$213.00
Purchase #3	$40.41	11.561%	$45.0818	$45.08	$45.10	$45.10
Purchase #4	$144.95	10.603%	$160.319	$160.32	$160.30	$160.30
Purchase #5	$220.64	12.739%	$248.7473	$248.75	$248.75	$248.70
Purchase #6	$41.63	10.209%	$45.88	$45.88	$45.90	$45.90
Purchase #7	$62.73	3.484%	$64.9155	$64.92	$64.90	$64.90
7 purchase totals =	$760.64		$839.5970	$839.60	$839.60	$839.50