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	$79.52	7.640%	$85.5953	$85.60	$85.60	$85.60
Purchase #2	$74.37	5.642%	$78.566	$78.57	$78.55	$78.60
Purchase #3	$121.39	8.141%	$131.2724	$131.27	$131.25	$131.30
Purchase #4	$243.89	8.537%	$264.7109	$264.71	$264.70	$264.70
Purchase #5	$31.86	4.102%	$33.1669	$33.17	$33.15	$33.20
Purchase #6	$176.43	8.135%	$190.7826	$190.78	$190.80	$190.80
Purchase #7	$117.26	13.520%	$133.1136	$133.11	$133.10	$133.10
7 purchase totals =	$844.72		$917.2077	$917.21	$917.15	$917.30