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	$7.47	5.799%	$7.9032	$7.90	$7.90	$7.90
Purchase #2	$97.36	8.458%	$105.5947	$105.59	$105.60	$105.60
Purchase #3	$173.90	11.807%	$194.4324	$194.43	$194.45	$194.40
Purchase #4	$216.99	3.478%	$224.5369	$224.54	$224.55	$224.50
Purchase #5	$195.83	9.601%	$214.6316	$214.63	$214.65	$214.60
Purchase #6	$164.91	6.613%	$175.8155	$175.82	$175.80	$175.80
Purchase #7	$52.52	5.352%	$55.3309	$55.33	$55.35	$55.30
7 purchase totals =	$908.98		$978.2452	$978.24	$978.30	$978.10