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	$23.40	12.441%	$26.3112	$26.31	$26.30	$26.30
Purchase #2	$70.42	10.824%	$78.0423	$78.04	$78.05	$78.00
Purchase #3	$109.63	7.631%	$117.9959	$118.00	$118.00	$118.00
Purchase #4	$164.39	10.732%	$182.0323	$182.03	$182.05	$182.00
Purchase #5	$127.61	7.439%	$137.1029	$137.10	$137.10	$137.10
Purchase #6	$225.76	10.449%	$249.3497	$249.35	$249.35	$249.30
Purchase #7	$55.72	10.201%	$61.404	$61.40	$61.40	$61.40
7 purchase totals =	$776.93		$852.2383	$852.23	$852.25	$852.10