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	$250.59	9.827%	$275.2155	$275.22	$275.20	$275.20
Purchase #2	$43.67	3.862%	$45.3565	$45.36	$45.35	$45.40
Purchase #3	$11.37	9.669%	$12.4694	$12.47	$12.45	$12.50
Purchase #4	$71.97	8.867%	$78.3516	$78.35	$78.35	$78.40
Purchase #5	$243.55	3.252%	$251.4702	$251.47	$251.45	$251.50
Purchase #6	$83.95	6.223%	$89.1742	$89.17	$89.15	$89.20
Purchase #7	$93.80	3.849%	$97.4104	$97.41	$97.40	$97.40
7 purchase totals =	$798.90		$849.4478	$849.45	$849.35	$849.60