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	$78.50	10.718%	$86.9136	$86.91	$86.90	$86.90
Purchase #2	$152.82	8.718%	$166.1428	$166.14	$166.15	$166.10
Purchase #3	$34.64	12.208%	$38.8689	$38.87	$38.85	$38.90
Purchase #4	$62.46	3.288%	$64.5137	$64.51	$64.50	$64.50
Purchase #5	$244.59	8.224%	$264.7051	$264.71	$264.70	$264.70
Purchase #6	$181.98	10.345%	$200.8058	$200.81	$200.80	$200.80
Purchase #7	$124.40	13.484%	$141.1741	$141.17	$141.15	$141.20
7 purchase totals =	$879.39		$963.1240	$963.12	$963.05	$963.10