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	$159.96	7.486%	$171.9346	$171.93	$171.95	$171.90
Purchase #2	$21.39	12.301%	$24.0212	$24.02	$24.00	$24.00
Purchase #3	$82.47	9.443%	$90.2576	$90.26	$90.25	$90.30
Purchase #4	$112.63	9.474%	$123.3006	$123.30	$123.30	$123.30
Purchase #5	$83.44	9.274%	$91.1782	$91.18	$91.20	$91.20
Purchase #6	$77.54	12.280%	$87.0619	$87.06	$87.05	$87.10
Purchase #7	$228.42	4.497%	$238.692	$238.69	$238.70	$238.70
7 purchase totals =	$765.85		$826.4461	$826.44	$826.45	$826.50