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	$126.86	10.361%	$140.004	$140.00	$140.00	$140.00
Purchase #2	$90.41	11.108%	$100.4527	$100.45	$100.45	$100.50
Purchase #3	$36.61	3.128%	$37.7552	$37.76	$37.75	$37.80
Purchase #4	$119.63	3.124%	$123.3672	$123.37	$123.35	$123.40
Purchase #5	$12.61	9.407%	$13.7962	$13.80	$13.80	$13.80
Purchase #6	$166.46	11.299%	$185.2683	$185.27	$185.25	$185.30
Purchase #7	$189.90	10.179%	$209.2299	$209.23	$209.25	$209.20
7 purchase totals =	$742.48		$809.8735	$809.88	$809.85	$810.00