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	$101.78	7.664%	$109.5804	$109.58	$109.60	$109.60
Purchase #2	$146.56	12.486%	$164.8595	$164.86	$164.85	$164.90
Purchase #3	$82.98	4.871%	$87.022	$87.02	$87.00	$87.00
Purchase #4	$181.84	8.705%	$197.6692	$197.67	$197.65	$197.70
Purchase #5	$13.89	13.869%	$15.8164	$15.82	$15.80	$15.80
Purchase #6	$100.97	3.371%	$104.3737	$104.37	$104.35	$104.40
Purchase #7	$12.96	12.188%	$14.5396	$14.54	$14.55	$14.50
7 purchase totals =	$640.98		$693.8608	$693.86	$693.80	$693.90