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	$157.56	10.134%	$173.5271	$173.53	$173.55	$173.50
Purchase #2	$16.32	12.144%	$18.3019	$18.30	$18.30	$18.30
Purchase #3	$246.37	13.373%	$279.3171	$279.32	$279.30	$279.30
Purchase #4	$51.47	4.191%	$53.6271	$53.63	$53.65	$53.60
Purchase #5	$236.60	5.529%	$249.6816	$249.68	$249.70	$249.70
Purchase #6	$29.73	12.755%	$33.5221	$33.52	$33.50	$33.50
Purchase #7	$89.87	7.500%	$96.6103	$96.61	$96.60	$96.60
7 purchase totals =	$827.92		$904.5872	$904.59	$904.60	$904.50